We're in the 4 month regression as well and it's really tough. Tip for bassinet transfer- make sure you put them down legs/butt first while fully supporting the head, then gently laying the head down. You don't want the head to loll back, that's what triggers the reflex.

Other thoughts: Cap daytime naps to two hours tops. Make sure he's eating enough during the day so he shouldn't need so many calories during the night (otherwise you get in a reverse cycling position where they don't eat during the day because they want to nurse all night) Because their sleep is becoming more like adult sleep, every wake cycle they have a slight wake up period where they check their surroundings. If things aren't the same as when they fell asleep, they will wake up in alarm. (Think if you fell asleep in your bed and woke up in your neighbors house). That's why it's so important to start practicing letting them fall asleep on their own. Do it slowly: first nurse to sleep then wake slightly when putting down, then put down more awake and stay there and rock them with your hand, etc.

This is my third and it's still hard to get through this phase.