I use a wallet of Satoshi (wos). Very easy to use. You can buy the bitcoin on an exchange (Coinbase, Gemini, etc) and transfer that to wos. Keep in mind that when you transfer to the wallet on your phone, the money is literally on your phone meaning if you lose your phone you lose your money In the wallet. So don’t put too much in the wallet. There may be a way to add an email so the money is retrievable.

https://www.walletofsatoshi.com/