You can use Unstoppable wallet. It has has the swapping feature and it supports bitcoin. It is still one of the best bitcoin wallet. But if you want to hold your coins, cold wallets are better.
Bitcoin Core? Space is not even a problem if you enable pruning. I see no reason to use something different.
He is not referring to Bitcoin Core. He is looking for a good wallet that he can swap bitcoin for USDT and swap USDT back to bitcoin.
Sounds like a very unsafe plan. Let's just hold his BTC in Bitcoin Core and, when time will come, move them everywhere he wants to sell them.