No I'm here! Sorry for the slow reply
3.5h I would say is probably on the shorter end of A times for this age group (
Average A times- BOOKMARK ME! ) so I might be tempted to push that a bit further and see if he goes down more easily for you. It's often a rough time for naps anyway around this age as the beginnings of the 2-1 transition kick in - not saying he is ready for one nap all at once! Just that's likely to be the direction things are headed over the next few weeks to months.
That might mean if you want to keep a longer morning nap that you will need to wake him from his second nap to keep bedtime to a sensible hour. From memory with DD at this sort of stage we were doing something like WU 6.30, Nap 10.30-12, Nap 4/4.30 for 30-45 mins then bed at 7, asleep for 7.30ish. Some LOs will be happy to go down a bit earlier and will take an UT afternoon nap and wake naturally, though that tended not to work for us very well.
He's often fussy and protests as soon as we put him in his sleeping bag, even though he's yawning.
This could well be him telling you he isn't ready to sleep yet. Tired signs become more unreliable as LOs get older and yawns can be boredom, accumulated tiredness, or even just habit if he is used to sleeping at a certain time. This may be especially true of the morning nap as that long dozy feed in bed isn't really stimulating A time, and I'd expect he could manage a bit longer awake before needing to sleep again.
'm now wondering if he's hungry again by the time I put him down for his naps. I realise maybe I should be giving him more snacks.
I would give him a good snack sometime before his first nap, if you push that first A time a bit then you could do it around 9.30/10am which fits nicely with your other meals and snacks.
With PUPD I think you need to separate the eating entirely from sleep. Fine to breastfeed before sleep is due, but I would do it in a bright room, not the bedroom, and a good 15 mins ahead of when you are planning to start the sleep routine. If you let him feed for 10 mins to get comfy, then stop and PUPD I think that's really confusing for him and will add to the frustration.
I would tackle naps and bedtime all at once yes, and the same for night wakings i.e. not picking up/cuddles/singing. I'd expect it to be really tough for the first couple of nights but then you should see some improvement. How are you feeling about it?