I need some baby advice

Tr

My son is 4 months old. He's still sleeping in our room, but in a bassinet. The little matress it has is a soft one. He's been in it since birth and sleeps in it just fine at night. During the day he sucks at napping unless in our arms. But every once in awhile he'll fall asleep on his own our bed and that matress is memory foam. So it's soft as well.

For the last 2 weeks, I've been crib training him and he's not a fan. As soon as I set him down in it, he instantly wakes up and cries. I've been consistent and been loosing my mind.

I took my pregnancy pillow and wedged him on it on my bed and started cleaning to not lose my mind and he fell asleep in it. So I put that in the crib the next day and he fell asleep in it for 2.5 hours. It was glorious. Yet nerve-wracking. I kept checking on him and had the baby monitor glued to me.

All the crib mattresses are hard. I'm thinking my baby likes soft mattresses yet that's a no no. I just don't know what to do. I tried the crib again with no pillow to see if he was used to it and he just cries. Have any of you mamas go through the same thing? Is there something on the market that I could use that helped you? I'm a new mom and between my "lovely" MIL grilling me that he should be crib trained and he shouldn't be with anything in it (which I get) but I'm trying to do what's best for him and I feel pressured and defeated.