It's best if you have a separate wallet for bitcoin and a separate wallet for your altcoins.
And why look for good self-custody wallets? Also, look for ones that are open source, not just any wallet that claims to be self-custody.
For altcoins, I know of
Unstoppable Wallet and Metamask; they are both open source.
For Bitcoin, you can go for
Blue Wallet or Electrum. They are also open source and both mobile-compatible.
Mind you, the safety of each wallet is also dependent on how you carefully handle the security of the wallet.