I agree with pp. You are over thinking it and over planning. The best routine will come from your baby, not you. Baby just needs to be given the rudiments of a good routine - set wake up time in the morning, 7 days a week, to give a consistant start to the day. To be able to go to sleep at the just-tired point and to get plenty of sleep.
This makes it very difficult to plan the rest of my day and is currently messing with all the 11am classes we are attending (or currently missing)
Are you on maternity leave or a SAHM? The benefit of experience has helped me see the bigger picture with regards to this sort of thing.
Because I'm not in a rush to "enjoy my time on maternity leave" (I'm a SAHM), there is no pressure to do stuff. With my youngest I knew that there would be loads of time to do the fun stuff with her once she wasn't having morning naps.
As soon as she dropped the morning nap we started - swimming, playgroups, messy play, children's cafe, music groups - all those stuff you imagine yourself doing when you have a baby.
But the benefit of hindsight taught me about slowing down, there is no rush. So when I had a baby and toddler at home, baby was tagging along to these things because I as going with toddler. But these weren't really for baby. Mostly baby slept through them.
When my older ones were at school and it was just me and youngest at home in the daytime, the benefit of hindsight shows that I didn't need any rush to "do stuff". Especially in the first year. The classes and stuff can wait until her days were more predictable. In the first year, there need be no rush or pressure to do everything right now. Right now often isn't the right time in the first 12 months.
a few weeks ago he was doing a 2 hour nap in the morning and an hour and a half at lunch then a cat nap at the end of the day, so getting 4 hours daytime sleep with a 7.30pm bedtime
I would suggest that from the routine you had a few weeks ago, the next stage would be drop the catnap and add that amount of sleep onto the nights sleep.
The amount if sleep baby needs between around 3 months old and 3 years old remains roughly the same. Certainly the reduction in total sleep is a gradual change. Rather than a sudden reduction in total sleep, its more the timings for sleep change. Here's my example from my youngest:
5 months old:
1.5h morning nap
1.5h afternoon nap
1h teatime nap
11-12h overnight (broken)
TOTAL: 15-16h
8 months old:
2h morning nap
2h afternoon nap
11-12h overnight (broken)
TOTAL: 15-16h
12 months old:
2h morning nap
2h afternoon nap
11h overnight (unbroken)
TOTAL: 15h average
24 months old
3-4h afternoon nap
11h overnight (unbroken)
TOTAL: 14-15h