Hi, I have been where you are! 
I actually used a daily to-do-list app, and put a list very similar to Pesty's on it, it felt good to tick things off. Be careful not to add too many things, about ten tiny steps maximum, over-ambitious to-do lists can feed anxiety. I found it helpful to think of it more as a "did-do" list, and every tick was a little pat on the back. Break it right down into tiny steps if you need to, no one else has to see it.
For what suits you, it might be helpful to think back over the clothes you had when you were more put together - what did you really feel good in, what always got you compliments - write down those items, and what was special about them - the type of heel on a boot, the cut of a pair of pants, the bright red of a coat?
Just start playing with these ideas before you buy anything, let that feeling of having fun with style come back.
YouTube has some good content to build enthusiasm, but do look for vloggers who are a similar age to you.
I started dressing well again by deciding on just one outfit - the thing I could wear almost every day, because my days were pretty much all the same (SAHM, school pick up, supermarket etc). For me that was a long sleeved wrap dress with boots. I bought two from ASOS and suddenly it was easy to get dressed and look okay without making decisions. Could you think of one outfit?
Best of luck on your recovery journey, getting to this point where you are able to consider this sort of change is an achievement all by itself.