Convertible car seat issues

My son is almost 4 and he’s still using his Nuna Rava. He’s very tall but he’s never had any issues with the car seat until recently. On the last two road trips we’ve gone on he’s been mentioning that the crotch strap hurts him, so I’ve been rolling up one of his sisters burp cloths to put between his boy parts and the strap. Does anyone know if this is even safe, and if it’s not safe do you have another suggestion to help prevent pinching on his crotch? We use the crotch strap pad that comes with carseat, but it’s not enough apparently. Please help! Also, we are planning to get another convertible car seat for his baby sister soon, so if there’s a different car seat that you recommend for tall boys we can just give the Rava to our daughter.