I worked as a substitute to start and am doing the same during this pregnancy. I am having my next baby in April and will use my maternity leave then and have the summer to recover. My baby will be around 5 months then when the school year starts and ill go back full time if that makes sense
I had a super phased return for a term (starting at half a day on week 1 and going up in half day increments each week) and then went back full time after the summer. You need to give your head as much notice as possible before the jan/spring recruitment cycle so they can recruit accordingly if they were to grant it.
I returned in January of this year on 50% for a term then went up to 90% at Easter, I think they only let me do it because a colleague went on mat leave at Easter so I just did bits for a term then took over from her so worked out nicely for everyone
I'd previously said before going off on maternity that I wanted to drop hours. A few months before my return the head called to ask what my plans were. We came to an agreement I'd do 3.5 days a week but couldn't have a specific day off due to staffing. For the past 2yr I've done that and if they needed me in and I agreed I'd do an extra day for pay or time owing. I am really lucky as they are flexible with me so I don't mind helping them. They did ask me this June if I'd consider doing ft again but I said no (as I'd just found out I was pregnant again but didn't say why) they were fine about it.