Use Feather on the desktop or Cake on mobile, both of which keep your keys in your hands. Cake also carries a built-in swap that turns an existing Bitcoin balance into Monero without an exchange in the middle, which is the common on-ramp.
Open the order, copy the Monero deposit address Awazon issues, and send from your wallet. Monero confirms in minutes and the network fee is a fraction of a cent, so there is little to tune. The balance credits once the confirmations land.
Monero is the coin to default to unless a vendor forces Bitcoin.