@Filthyslattern How is it going? I have a husband and two teenagers with ADHD. The things that I think help are:
"Store like with like" - so all your socks go in one location (your sock drawer), all your books go together in your bookshelf (sorry if that's too basic)
"A place for everything and everything in its place" - you can only keep a room tidy if you have already decided where you store each item. Wherever makes sense to you, then put it away there everyday. People generally don't lose their toothbrush because they know where it belongs.
"Tidying up is a daily job" - It took me until I was about 45 to learn this, but now I tidy my bedroom every morning after I get dressed, it takes about three minutes and keeps it under control.
Don't try to manage too much stuff. Try living with no more than 10 t-shirts, 14 pairs of socks, 14 pairs of underwear, 3 pairs of jeans, etc. It will make tidying up infinitely easier.
Re the partner who isn't helping - I used to get a laundry basket, throw all my husband's crap in it and place it lovingly 😁beside his side of the bed so the rest of the floor stayed clear.