Absolutely fuck batch cooking - get yourself down M&S or whatever and get a decent ready meal or two for the nights you're by yourself. Do not waste what limited time you have bloody batch cooking.
Where's your partner in all this? Does s/he only have 30 minutes a night to themselves as well? If not, they need to up their game - all decluttering, childcare, household chores etc does not fall on your shoulders alone.
If you've the annual leave spare, I'd take the week off together and blitz the house. Be vicious, no piles of crap waiting to go into the car to eventually maybe make it to a charity shop. Charity shop that week, or it goes in the bin. Hire a skip if you need it, or book a tip run. If the clutter is really getting you down this might make a big difference.
Yes to exercise. Doesn't have to be a lot, even just a wee walk is good for your mental health, or 30 mins stretching, or anything at all. BUT do it for the endorphins, not as another stick to beat yourself with if you're just too knackered. Exercise is a privilege, not a punishment.
Streamline everything - online food shopping, who cares if it's the same things every week, long as there's food in. 'Dump' baskets all over the house, and on the stairs - they contain the clutter and make it look tidier, you can corale them once a week. A darks and lights laundry basket = no sorting, just shove it in when one fills up. Fuck ironing, hang it up in the bathroom while you shower. If you can amazon prime it and avoid a trip to the shops, do so.
Looks wise - high maintenance to be low maintanance. Exfoliate body 1x per week, decent moisturiser. Gel nails (if you like them, otherwise just file etc at home). Isle of Paradise 30 min fake tan if you hate feeling pale. Learn one hair - up style that isn't just a mum bun (loads on youtube). All these things make me feel better and a bit more polished when I feel like a frazzled mess.
But sorting out my partner pulling their weight and the exercise would be my priorities if I had to pick one!