mmm... this topic again.
[not complaining - my jumper(s) make me very happy]
So here are a few videos of interest, from the tube of you:
https://www.youtube.com/watch?v=qDkafZhvfcs
https://www.youtube.com/watch?v=dV8FeXge28c
Outside is your best bet. Indoor installation *is* possible and I've done it -- I live in a cold climate so you know very well I'm not doing much outside in the snow -- but unless you own your home and don't mind some structural alterations, go outside. I've used solid trees, a not-currently-used-for-trains railroad bridge, and some weird beam thing that was attached to my deck at a place I rented for a while.
You've got a few options for bounce. Metal springs and bungees. They feel *very* different from each other. Both have safety considerations. I prefer metal springs, so I have more to say about them.
BUNGEE CORDS -- noteworthy bits: The fabric/cloth-wrapped ones will be safer than bare rubber, because the fabric will stop the stretch at a certain length. If you're "bottoming out" often (reaching the fabric-enforced limit) then you DEFINITELY need more bungees. They come in varying diameters with varying "bounciness" so there's no definite rule for how many you need. I have a set of *eight* together that work for me. If you buy "tie-downs," you DO NOT want to use the original hooks that come on them -- the cord itself pulls through them very easily. Buy bungee cords 3x longer than you think you need, and loop them back and forth so there are three sections next to each other. This reduces the stress on the actual ends. Bungees' benefit is that the length is infinitely adjustable, so there really isn't much to discuss -- measure the length you need, multiply by how many you think it'll take for your weight, and buy the fabric ones in case your math is wrong, you'll just end up with rope instead of pain.
I *greatly* prefer the bounce of metal springs, but there's a bit more to consider, because they come in specific lengths and because, with few exceptions, they don't have any built-in stretch limit.
If you've chosen to install indoors, you don't have much for traveling distance. You want short springs. If you use trampoline springs, take your weight, divide by 40, and use that number *next to each other*. If you want longer travel, double them in length. (examples: I'm 120 lbs, I need 3 springs. If I want to travel further, I need 6 springs -- three strings of two each).
If you're outdoors, or in a place with a *very* high ceiling, garage door extension springs are a very viable option. They are rated by the weight of the door - buy a set that matches your weight, or the next size up. You will be using two of them, side-by-side, see videos.
IMPORTANT SAFETY BITS: the springs (usually) come with a piece of steel cable and some fittings. The idea is to run this piece of cable down through the center of the spring and secure it on both ends. This takes care of two safety-related issues: one, it limits how far you can stretch the spring, so you won't break it if you have a particularly heavy dinner, and two, if you do manage to break one, the cable keeps the loose end in check. In practice, I often replace the cable with heavy rope.
For hardware, head to any hardware store and pick up some "carabiner" clips, rated AT LEAST twice your weight... If it doesn't have the weight rating written on it (or the package), don't buy it. If it says "NOT FOR CLIMBING" then run far far away.
Attachment -- my favorite "easy" attachment point was the railroad bridge. I simply looped a piece of heavy chain over one of the ties and carabiner'ed a spring to each end of it.
SEAT/HARNESS: As another mentioned, you CAN use a climbing harness.
https://www.youtube.com/watch?v=RoiIUHwPsqg was fun... but as you might note, it's not much like an actual jumper. By far the best readily-available jumper-style seat out there is the "Airy Fairy" swing. They're a bit spendy sometimes, but if you watch the bay of E long enough they usually pop up in the $50 range, sometimes even cheaper on the list from ol' Craig. Other options... if you're small, you can try to find the special needs version of the Merry Muscles, works up to a 30" waist or so. I made an enlarged version which I initially offered to make more of but I could never really find time to make that work -- if you're good with a sewing machine, I can send you that drawing. HABA has some other largish-looking "baby" swings I haven't tried yet. Lastly, and this appears in one or two of the videos I posted, if you get one of the frame-type backpack carriers with a "square" seat, you can sometimes remove the seat from the frame and that works rather well.
If you search the forum, this topic has been brought up a few times. I'm always willing to discuss as well.
DON'T BE SCARED. I point out all of the safety things I've encountered, and how I've deal with them, and that can sound daunting, but, in the end, think about it -- you're deliberately jumping in a harness that lifts you up but each time lowers you enough to touch the floor. You can't possibly fall any further than you're already deliberately jumping, because the floor is there. If you hang your springs with two clips from two eye bolts and each is rated to twice your weight, you've got a safety margin of 400% -- the springs aren't coming down. The cable through the middle means that you won't over-stretch them, and if one does break, the cable will catch the end, so it's not going to slingshot at you. The worst /likely/ failure is you falling, a few feet - the height you were jumping anyway. I've had it happen, it's how I learned what works and what doesn't. I'm still here, still in excellent health, and still jumping.
