Hi, welcome to the site! I'm a newbie here, too, but that's partly as I've been out of the scene for a couple years. I do have an idea of what you're talking about, but please forgive me if I'm a little skeptical...
I've been into diapers since I was 13, but as there were no disposables for teens back then, contented myself by occasionally making homemade diapers. I bought my first disposables in my late 20's. In 2003 I decided to wear diapers as often as possible, and eventually settled on trying to un-train myself enough to start wetting the bed. It took about 5 months. It wasn't that I was sleeping through the night, but that I was waking at 4 or 5 am with a strong urge to pee, and realizing I was already wet. This continued most every night for about 2 weeks, at which point I got scared and put the diapers away. I was concerned about the sleep-wetting continuing, and for a while, brought a diaper with me when I slept away from home. It never happened.
If you read-up on the process of un-training your bladder, lots of people say there's a strong psychological aspect, and I definitely agree. Your brain knows when "all systems are go" and when you really don't want it to happen. Over time it is possible to get into a pattern of bedwetting, and after that start to see some physical issues like a weakened sphincter muscle. For me, though, this required lots of conscious effort, not to mention some subconscious effort. I've read lots of posts on [That site].com where a person gets put into a diaper at a friend's house and immediately wets the bed that night. I don't believe it. In your case, maybe your brain is exceptionally succeptible to the idea, but if you're saying you went from totally continent to needing pullups durig the day in a matter of weeks or months...sorry, I'm skeptical.
FYI, I started my bedwetting experiment again just a few weeks ago and had my first accident Saturday night, so it apparently is easier the second time around. I'm not opposed to wearing (and using) diapers or pullups during the day (ie. to work), but have resisted it so far because of the possible long-term commitment. Maybe I'll find day-wetting isn't so hard after all? Soiling a diaper involuntarily also seems like quite an undertaking, but then I've never tried that route. (What seems hardest is that most people would get just one chance per day to practice.)
As for better night diapers, you can get cheaper night diapers by switching to Wal-Mart's Overnite briefs. Despite my username, I don't plan on buying Depends again, if I can help it, as the Wal-Mart diapers seem just as good. I wear one of these at night, with a Depends Boost insert, covered by a pair of white jockey shorts (ie. Hanes), covered by plastic pants. I sleep on my back without rolling, and very rarely leak. So my suggestion is that if you don't want to mail-order diapers (why?), get yourself some plastic pants, which I'm sure are available at local medical stores. As for my favorite high-capacity diaper, a few years ago I settled on Tena Super's, as a good mix between capacity and price. But they do swell up a lot when soaked, particularly in the crotch, and it can take some effort to avoid waddling. I have no idea hw common they are locally. Modern Attends are apparently are no better than Depends, and may cost even more.
Hope that helps!