"the children, housework, cooking and so on fall largely on me. DH is good. He does do his share but in all truth and honesty isn’t around much. In fairness this is also true even if I was to work full time so I guess that’s personal to me / us."
"there’s only disadvantages to me working part time - less money and career prospects"
"I have children on the two days I’m not in work and I do struggle to get anything done. I end up having to try to do it when they’re in bed"
"benefit my children and they’re the important ones but it is a bit rubbish for me."
When a PP suggested you and your husband each do 4 days you said "It would be nice but isn’t an option." Why is that?
If it's best for the children to have a parent with them 2 days of the working week why can't those two days be shared between their parents?
What I'm trying to say by highlighting the key parts of your situation is you take on the majority of your family's labour - cooking, cleaning, child rearing and I'm sure the "life admin" too. You acknowledge even if you worked full time you still likely would and while you say this is personal this exact scenario plays out in millions of heterosexual relationships hence "the personal is political". And the inequality within your "partnership" is being modelled to your children too. They're learning mothers do all the work even when they work ourside of the home too, fathers "help".
You say he does his share but what actually is his share particularly if he's not around much? I'm not trying to be negative here or attack your husband or relationship because this isn't just you it's the default for women and it's harmful. You've acknowledged yourself this "choice" has given you less money and less career prospects. So if you did increase your hours is it possible for him to decrease his and take on more responsibility at home? How long will you halt your carerer for? Until the children are in full time education so possibly "only" a 5 year gap and knock to earnings and progress? Or till they're in secondary school or finished education? So a decade or two? The thing is for women is not just the 2 days pay lost although in the immediate term that is what is balanced alongside childcare costs when making the choice. It's the years of career stagnation you're taking on and the financial hit on your lifetime earning potential which is the big thing.
Right now you're paid working 3 days, doing full time child rearing 2 days. Evenings of all 5 days either doing work for your paid role which is in effect unpaid as you're having to do it now outside of normal working hours and/or housework. You're working 5 days and 5 evenings a week? For the salary and career prospects of 3 days work. Your husband is working 5 days for the salary and career prospects of 5 days. How many of his evenings are spent on housework when the children are in bed? Does he batch cook while you're doing your teaching admin? Does he sort the upstairs which is weighing on you? Is is 5 days of salaried work and career opportunities only 5 days of work and zero evenings?
Maybe examine your life and who it is benefiting most from your choices as that person should really be you or at least you jointly with your children. If it isn't, why is that? You matter. Your career matters. Your health. Your leisure time. That all matters too. Children don't stay children forever and the consequences of being the default parent, the default house manager well they go well into the years after your children have left home. They go into your pension and savings and financial independence should the worst happen.
I guess what I'm saying is you're not being unreasonable to feel you have a poor deal and the worst of both worlds working part time but also how can you change this?