You're overthinking this, honestly. I think 99.9% of others have done the exact same thing too, so don't fret over it. Before becoming disabled and physically (medically) NEEDING diapers (lower spinal destruction L2 through L5/S1 + nerve damage, numerous surgeries from discectomies through a morphine pump implant, spinal stimulator implants etc. etc.) I too LIKED to wear/use diapers. I had these desires, OVER POWERING at time since before I was fully potty trained not much past the age of 2! I learned how to "poop on the potty" and knew when I had to go right around 2 years old, but I truly LOVED going to sleep in a "loaded Pamper". It was a cat & mouse game with my Mom for most of a year until I got a handle on wetting well before I was 3. She'd MAKE me sit on the "potty" until I went and when I knew I had to go but wanted to sleep in a messy diaper I'd sit there for as long as she made me, insisting I didn't have to go! I did that quite a bit and remember at least 3-5x quite clearly actually. As soon as I'd hear her footsteps going down the stairs after being put down for bed at night or for a nap (usually waited til night time so I could get the "full effect" I'd wait for as long as possible (she caught me intentionally doing this more than a couple times) until I literally was about to pass out from boredom or simply being tired and then I'd let rip! I know for a fact the last time I did this I got dragged out of bed whenever my Mom & Dad went to bed, changed and spanked because my Mom made me sit on the toilet at least 3-4x throughout that day.
Fast forward to after getting caught for the last time when I was 7-8...I'd line my underwear with a LOT of TP, fill my pants and play in the bathroom. Got caught doing that A LOT, but this time was different as I was forced to wear Pampers for the next 2-3 days AND go outside to play with the neighbors, my brother etc.. The Pampers came nowhere near close to fitting me and were held on with black electrical tape wrapped all the way around my waist and I was made to fully use them. Thankfully I didn't have to "go poop" until after we were back in for the night. I had my balls busted about that by a lot of people until I was at least 10...by the time I was 12 I was lifting, wrestling, playing football (football started when I was 8, wrestling when I was 10, lifting @ 12) and became one hell of a "banger" and no one that knew me made fun of me anymore. I never did get caught again as far as I know.
I used to obsess over buying diapers much like you are now. For years I was always able to satisfy my needs by snagging a Pamper (or 4) from my best friend's house as he had 4 younger siblings and we lived at each other's house. Well, everything eventually comes to an end and I was 13 when I bought my 1st pack of Ultra Pampers Plus.....spent at least a half hour paralyzed by fear inside of a small little store to the degree the cashier and her friend couldn't keep straight faces when I finally got up the guts to grab a pack, take then to the register & pay for them. It really took a LONG time to get past that fear.
Now fast forward to 2004...in Jan 2004 issues I picked up while in the Army (incident began in Aug/90) came to a head and turned into 24/7/365 chronic problems with indescribable 24/7/365 headaches being at the top of the list followed really closely by frequently indescribable back pain to the point by Sept/Oct '04 I couldn't even stand or walk. I had been wetting myself unknowingly & uncontrollably since maybe June and somehow was able to lie about that, at least I thought I was good at hiding it. I was deathly afraid that I was literally dying as I went from a 232 lb ROCK who was benching over 500lbs, squatting just shy (literally) of 1000lbs, working 50-60 hours a week at my business, fishing a minimum of 15 bass tourneys/year on top of having two very young sons, lifting every other night (I'd take off 6 weeks or so each summer), doing everything required around the house, kept the soon to be ex happy to literally not being able to stand or walk without a walker and sometimes incapable of even doing that.
Well, not only being older and not caring so much. I mean, everyone who knew me knew of my issues as they came on so brutally fast so my entire family, at least 2 dozen good friends, every medical professional etc. knew of ALL of my issues. I was buying Molicare from a local medical supply store by this time (after a nightmarish experience relying on depend!) and I got to the point where I didn't even take them to my car (or have them taken to my car/minivan (couldn't get in/out of my truck) without bags.
Today I do my best to conceal what kind of "underwear" I have on though never had any issues with anyone pointing it out, people talking behind my back etc. No one pays any attention so long as you're not flaunting anything AND you act normal as to not give them any reason to wonder why you're acting very nervous, anxious etc. That last line is CRITICAL. Trust me on that!
You will get used to buying these supplies and no, don't even bother making up bullshit back stories as they're a dead giveaway that you're doing something out of the ordinary or trying to hide something. You need to act as if this is nothing and you do it all of the time.
I have more to add but have a slew of Appts today and have to jet shortly.
Let me know if I can be of any assistance to helping you learn to not care so much so you ARE able to relax without even thinking about it.