It gets talked about to death but for me it really was the simple things.
Drinking enough water. Quantity is key, forget about all the negatives of flavourings etc and figure out what will actually make you want to drink, and stock up. For me it's Ribena/Whittards powdered fruit teas. Sure they have sugar/are expensive for everyday, but compared to dehydration it's still massively helpful.
Eating well, and the food you like to eat. If I'm feeling shitty, eating a cheap salad isn't sustainable if all I'm craving is takeaway pizza! So I get used to gently talking myself into reasonable swaps, like getting a Wagamamas or anything with loads of veg instead of ordering pizza, or making myself a cheesy jacket potato instead of devouring a share bag of crisps. I always try and go for things that balance what I 'want' with what I know is better for me!
Walks/working out and fresh air. If going out is too much, open a window. If going to the gym is too much, put on a Taylor Swift (or whoever you like who's upbeat!) dance/exercise video on YouTube.
On that note, upbeat positive music as you're doing daily tasks is such a game changer for me. I like putting on dance hits in the shower and pretending I'm actually an award winning singer performing to a sold out crowd. Anything that makes you smile is worth it, regardless of how mad it might seem!
If finances allow, little treats are well worth it wherever you can afford it/want them. A bar of your favourite chocolate, nice hand cream, a new bag. I like things that I can keep using so continually perk me up.
Don't try and fix everything at once. What you're doing is bloody hard, and even if you just do one small thing a day to improve - or even think about it! - you're on the right path.
Good luck 💐