Thank you everyone for all the other suggestions. I'm starting to think that, if I use Bitcoin Wallet, then I don't really need to use Coinbase?
You can use any bitcoin wallet you wish, provided it is one of the ones listed on the
official website, such as a hardware wallet, desktop client, smartphone wallet, or even a web wallet, like CoinBase (not recommended for large amounts or long-term storage). However, you will still need to use an exchange, such as Coinbase, to buy cryptocurrencies or convert them back to fiat. There are also other types of exchanges, such as P2P exchanges and decentralized exchanges, or you can simply exchange currencies in person.