Individually playing

I am a stay at home mom. I’ve been home with my 21 month old since he was 4 months old.

We play together ALL the time. I love seeing his smile and seeing him learn new things.

I am now 21 weeks pregnant and it’s getting hard for me to get on and off the floor to play with him so, I’ve spent a little more time on the couch. I’m noticing my son is just following me every where. He brings me toys and crayons and puzzles and of course I play with him but, what can I do to make him go to his room and occupy his self. He loves his room snd loves his toys but, he always wants me to play with him. When the new baby is here, I’m unfortunately not going to be able to give him all my attention 100% if the time and he needs to learn to go occupy his self. Any tips and advise?? My sister advised me to baby gate him in his room to make him stay in there to play but, I don’t want him to feel like his room is a place of punishment and isolation. I want him to just willingly go in there and have fun