Crib bumper?

Mamie

So I woke up today to both my sons legs sticking straight out between the slats in his crib (it was actually quite funny) but he managed to flip himself onto his side a little. I’m worried about him hurting himself.

Anyone have any suggestions about maybe using a crib bumper or lining or something to keep him from poking his feet through? I’m a little wary about putting anything in with him. He’s 12 weeks old.

Thanks!