Ironically, it looks like I went to register to post to a thread that has been locked. Ah, well. Moving on.
My main goal here is to be able to have you lay in your bed and wet yourself as you want, in a diaper, without it being 24/7, by six weeks. Why six weeks? It could be sooner, but I'd say six weeks "just in case".
First off, find a small cup, one you can keep with you around your sleeping area, bed or otherwise. Then, fill the bottom with a small amount of warm to cool water. Whatever you find comfortable.
Next, you will need to set it close to you as you are using the toilet. I'd suggest sitting down. Just before or as you urinate, dip the last three fingers of your non-dominant hand into the cup. Remove them and dry them off as you finish. If you want to do more than urine, that's your prerogative, not my area of expertise. And that's all you have to do for two weeks, ever so often.
After a while, you will find yourself naturally relaxing your bladder and urethra when you dip your last three fingers. Personally, I would advise against dipping every single time you use the bathroom, for a couple of reasons. The first one being, you may not always be able to dip your fingers, because of life circumstances. The more important reason being that if you don't do it every so often, it will allow the natural reflex to become voluntary, instead of instinctive. That, and your body might decide that you have to dip your fingers, which could be troublesome.
Now, after you have your bladder naturally relaxing at the dip of your fingers, then you would start wearing diapers, while on the toilet. This helps your body know that it's all right to use the diapers. Again, you still dip your fingers, up to two weeks, until you're comfortable with it.
After this, you're now ready for laying in your bed. Your body has gotten used to dipping your fingers for wetting, at your choice, and you are in a diaper, which your body knows it's safe to wet. Naturally, there might be some hesitation at first, but once you know, mind and body, that it's "safe", then you'll start wetting before you realize it. After a while, you will be able to wet yourself on command, without the finger-dipping, since your body will be able to relax, but can still hold it in, because you don't want it at that moment. Keep in mind, this will likely weaken your bladder at night, but you still have that control to keep it in.
By all means, if anyone has a success story, I'd love to hear them. Just remember, for a proper job, it'll take about 6 weeks. It also helps reassure those who are quietly interested. You know who you are.
Also, for those interested in the psychology of it all, read the spoiler below.