Do you have an Angelcare monitor? I've found that the temperature can be out 2-3 degrees at a given time. It's almost like the monitor only takes a snapshot of the temp every hour or so. I suspects it was inaccurate because it's readings didn t' feel right.' A gro-egg confirmed it was out of whack by 2-3 degrees. Which depending on what you dress bub in its enough to cause cat napping or early waking.
Depending on what tog your sleeping bag is bub could be too cold? 1-3 blankets doesn't seem like a lot.. Have a squiz at the SOS bedding guide link. But above all to by what your bub feels like. Touch the back of bubs neck. Bub should never be sweaty but should be warm and toasty.
Good call stopping using the fleecy onsie. SOS recommends using only cotton/bamboo bedding (clothes, sheets, mattress protector) as other materials can cause sweating. Plastic backed mattress covers are one of the worst offenders.
15-20 minutes on the playmat is pretty good: that's the same as my DS2. I find if he gets bored giving him something else to do helps (eg put on tummy, put in bouncer, pick him up. Basically changing it up every 15 minutes or so. Your bub seems to sleep quite well at night for 12 weeks.
Do you dreamfeed and use a comforter?
Please try not to worry too much if it's not all totally going to schedule. It's ok to be 60% there.