Have a big bunch of 
So many fantastic suggestions above. The thing that helped me most (when going through a hard period) was making steps to slowly lift my self esteem. It is tough and it sounds like you are already doing so well with the gym. I find yoga and meditation really help. Somehow it lifts the spirit, and adds to physical strength. I like slow and steady yoga - like vini or hatha. It doesn't have to cost a fortune. Your gym might offer it as part of your membership or a local hall or school might have drop in classes. Or there are a few good dvds and books which are handy for when DCs in bed.
For meditation I bought a couple of books and downloaded some apps.
A hobby really helped me too. I signed up to an art type course - something I loved pre D.C.. But can be tricky with childcare.
Nice hair products might help too. I splashed out on a Bumble & Bumble curl primer with Boots points. I'd saved the points for an emergency. But thought one day - why not. It lasts 3 times as long as a cheaper product. Smells fantastic.
And second all of the above. Go to a fair few make up counters and get them to help. I look for the smiley people working who look kind and patient. If they are in any way abrasive I politely go somewhere else. Take away testers to experiment at home in different lights.
Style wise - if you are not sure what look you want yet trawl things like Pinterest and save your favourite looks in your own clothes board. You can then add to it, and use it for inspiration when shopping.
Sample sales can be good for new clothes. Sometimes large brands hire a big Town Hall or similar and sell off past season stuff or samples. Hit and miss price wise but some bargains to be had. Look for clothes swap events too (tho often in eve and can be difficult with childcare).
Sales - Boxing day online or even Christmas night for the better quality bargains. Like maybe one nice coat. But depends if you can face going online after a busy Christmas day. Christmas eve after 11am sales in shoe shops and similar. Sometimes they slash prices ready for opening after Christmas or to tempt last minute gift hunters. Plus this way you get in early and have choice of the better stuff. Come a day or two after the choice may be limited. Also go back towards the end of the sale period. Sometimes people return unwanted goods - and they go straight on the sale rail.
And finally some advice from my lovely old Granny who had at times a difficult life. 'Always have one good quality tidy coat, one good stylish pair of shoes, and a neat small handbag. No one will know what's underneath''. She also used to say 'A lick of beautiful lipstick and a bit of rouge on the cheeks will lift you up and arm you well'.
Good luck OP. You are doing brilliantly.