You can't do this long term though. Not paying to work full time only applies for a short amount of time. It never "pays" to work zero hours.
You aren't interested in finding the optimum amount of work you can do, to both increase your income without penalty and get back in the workplace? You're not interested in thousands of funding whilst being unclear how you'll pay under £1000, mainly subsided rent in the future?
It absolutely pays to work. So, when I have no childcare costs in September, I will be increasing my hours. Because in order to still get CA, I'd have to cut my hours severely to only take home £602pcm. I've already secured this increase and a pay rise, by having my foot in the door with my low hours I work now. I'd have been able to do so even if I was only working 1 day a week. It's about having your foot in somewhere as well as the money.
I suspect, you will be putting in a claim for DD DLA in the next 18mths just before DS hits 16 and converts to PIP. Then you will have potentially another decade or so of the same financial situation via DD. You do need to consider her being refused, or even DS being refused PIP. It's always a possibility. The loss of DLA/PIP and CA would lose you just under £900 a month. That's huge. And put you into a different category of expected to work for UC. Even if you think it's nailed on, as you've seen from your current award looking wrong, you can't assume anything. And then, when she hits 16, then what? Cross everything for PIP for her? It's a risky way to live.
I get you don't like looking at it. But you truly need too. Full time isn't the sensible answer right now, very short term, very part time would potentially be. Then increased part time. And depending on what happens with DS/PIP, DD/DLA changes what the best route would be.