Since moving out into this supported housing gig, I've managed to do a great job of keeping it pretty clean and tidy, all things considered. (like having a messy flat mate) Before hand, I wasn't the tidiest person, nor the cleanest, but there were times I did stuff... like, even my mess was organised, I think. xD

Anywho, I manage it because, and I know this will sound obvious, but I basically clean up straight after I do something. If I spill something, I clean it there and then. If I use a plate, I take it into the kitchen, wash it, and put it away as soon as I can. This sort of habit is a nice routine and makes those other moments, like cleaning the toilet, bathroom sink, kitchen worktops, taking out the bins, etc, a bit easier to manage. I also find my other routines, such as working out every night, to be very helpful. Dunno if any of that is of any use to you, but that's my experience.

As for your current, specific situation, I'd suggest you start somewhere... little bit by little bit. As long as you're sorting more mess than you're making, you'll eventually get somewhere. :P

Getting in someone to help out would be great, and probably help prevent you letting things slide in the future. I'd help out if I were remotely near you, but I'm very likely not. xD

If you're in the UK, I believe there are people that can help, organisations and stuff, if your mental health issues are really affecting your ability to sort these things out. There may be similar options in other parts of the world, but I'm unfamiliar with those.

I guess I'm lucky, although depression screws me up, I tend to only get so bad before I go "That's enough! Must clean!" lol.

Best of luck.