I used Desitin with zinc oxide with my dog who didn't lick and it was the best thing I used. You don't have to put it on with every change, it clings to the skin well and you just butter a little more on as needed. You mentioned you had tried the disposable male wraps. I'm glad you said that because I haven't tried them and didn't know how good they are for a disabled pet. It sounds like they might be better for a dog that is just marking and not voiding a lot of urine.
Poise pads are really absorbent if you use them inside a washable belly band. I buy either the second highest absorbency or the highest for my 8 lb dog. On Poise they show the absorbency by water droplets. I buy the ones that are a 5 or a 6. 6 is the ultimate. I find I can cut the 2nd highest absorbency pad (5 droplets) in half and get 2 diapers out of one pad. The ultimate (6 droplets) pads are wider than the other absorbencies. With the highest absorbency pad (6), I can cut it in 3 parts and get 3 diapers. When you cut it in 3 pieces, the middle piece has 2 unfinished edges where you cut it, but it still works because for the most part the pad hangs together and does not spill out the filling even with 2 unfinished edges. If you buy a different brand, like Equate from Walmart which is supposed to be similar to Poise, it seems to have a different filling (kind of a sand almost) and is not as good at hanging together after you cut it in half, it is more likely to leak and be a bit messier. Of course you don't have to cut them in half, you'll have better coverage it you don't, but it might be an option.
I am still thinking about his bedding and the memory foam. I don't know the answer, just thinking out loud without coming to a conclusion really, since I've never had this exact situation but I can picture it very well from your description. It seems like if he could have something to dig his foot into, it would help him get up. In that case you would want something his foot would not slide on. I have no idea if this would work, quite possibly not, but I wonder if he had some booties with a good traction sole, if he could push himself up in bed. The booties would at least protect him from scraping his toes by friction if he tries repeatedly. Since I have never tried it I don't know, and I hate to make a suggestion that involves someone spending money on the off chance it might work when there is an equally good chance it won't. But I don't have a better idea. It would involve finding boots that really have major major traction, AND boots that will stay on the feet of your little 6-lb guy. If he has a slender foot not much bigger than his ankle, it will be harder for the boots to stay on. If he has a foot that is a little wider than his ankle, they will stay on better.
The other thing is, you don't want him to be miserable wearing all kinds of unfamiliar clothing like belly bands and boots, but if it could somehow help him, then hopefully he can adapt. It's good that he already is familiar with male wraps, yay for that!
It's too bad the Anipryl didn't work. I've heard it's kind of expensive and doesn't work on all dogs, but you don't know if you don't try.
This article suggests a couple of alternatives, but I have no experience with them.
Totally off the subject, but I just want to say I've been putting a diaper in my one dog in a certain way for 10 years, and
just today I found an easier way for her, so sometimes just doing something a little different, or being brave and trying something when you think it's not going to work, can actually work out.