I don’t think you need to give up your career to get him through the primary years.
Being a teacher means the obvious pro of having the holidays with him, so whilst he might have to do wrap around every day before and after school, you won’t have to do holiday clubs. As a solo parent, this will be a good money saver and much easier. Remember most other jobs will be all year round.
I mean obviously most parents are not teachers and make it work. Im just saying unless you really are miserable being a teacher I don’t think it’s worth throwing your career away just because of a few inset days.
Right now, tricky yes. But what may well happen is, as your son makes friends, you might be able to ask for favours. Offering another family a day of childcare in the holidays (which you have as a teacher) in exchange for help on inset days. Im sure something like this can be worked out as you go through. Not all insets will collide with his and some will.
Does he have any nursery friends or such you can ask for the first lot? Anyone you can offer taking their kids out a couple of times in the summer if they can have them on those insets?
Failing that, is he at preschool / nursery now? Could they have him those two days? At my old nursery we sometimes took new receptions starters back for those as hock days in the first term if we had space.
Do you have any connections via friends or family to students who would be willing to babysit for the couple of days?