Thanks guys. , I really appreciate your comments. I muted the baby monitor last night by accident which meant I only woke when he fully cried. Hey presto, we both slept better!
I think there are a combination of factors at play - me rushing in quickly, him used to me helping him , and something waking him. I will definitely look into the acid/meds tip, thank you. It makes sense. We're about to buy a new radiator for his bedroom in case the noisy heating is waking him - desperate or what?!
Today we are having a shorter A, extra feed and early bed plus I'm going to mute the monitor again!! Thing is, dd has a party today which is going to mess up ds naps. It's so hard to meet the needs of both kids. Stay home and baby is happy, go out and toddler is happy.