Just looking over what's happened over time I thought it might be useful for you to see a possible 1 nap routine.
This is based on a few things such as:
- he wanted to sleep longer at night and can do 12.5hr or more night sleep but is now reducing his night length
- he appears to be waking earlier and wanting a longer first A time, delaying/refusing first nap until later
- he can do a good long 2hr nap
- he seems to be reducing his first nap length to 1hr or 1.5hr rather than 2hr suggesting he could do with a bit longer A time
- he was comfortable at 14.5hrs total sleep in 24hr, but now he is reducing his sleep to more like 12.5-13.5 total in 24hr
This is how your day could look:
WU 8
A 5hr
S 1-3 (uncapped, it's ok to sleep longer, even 3hrs is fine)
A 4hr
BT 6.30/7.00 (if he took a 3hr nap BT could be 7.30pm)
night 13 - 13.5
overall sleep 15hr+
My thoughts at this point are that it may be worth moving to 1 nap relatively soon to retain the habit of a long night and a long nap 1. Although he is very young for moving to 1 nap, my slight concern is that if we wait too long he may continue to shorten his night and shorten his nap which then could make it a bit harder to get those back into place.
I would imagine an interim routine like this for the overall transition to take approx 10 days
days 1 & 2
WU 7
A 5hr
S 12 - 2
A 3hr
S 5 - 5.30
A 2hr
BT 7.30
days 3 & 4
WU 7/7.30 (not capped)
S 12.15 - 2.15
BT 6.30
day 5 & 6 (morning WU may be later by now)
WU 7/7.30/8
S 12.30 - 2.30
BT 6.30
days 7 & 8
WU 7.30/8
S 12.45 - 2.45
BT 6.45
day 10...
WU 7.30/8
S 1 - 3
BT 7
I know the best approach for you, and I think for your LO is a regular routine, you both seem to thrive of it. You may find LO can transition much quicker than this because he is so adaptable.
See what you think and maybe talk with DH about the transition period and the change in BT.
It could be possible to get back to a 7.30pm BT after he'd settled into one nap and when we can see how long a nap he'll take and how long a night he wants to do, after all every LO is individual so we are working with what we know but also with the unknown too