Infant support seat

Can anyone recommend a good infant support seat/cushion that can be put on a couch. My 15 week old has been trying so hard to sit up on his own and gets very frustrated about it so we’ve been having to prop him up with pillows behind his head while he’s in the boppy. He likes to sit straight up like he’s a big boy lol We have a floor seat but it’s way too big for the couch. I’d like something that could be sat next to me. He can sit without falling over as long as it has a high enough back on it.