UI automation is necessary for accessibility

My preferred one would be Monero. It's technically beautiful. It's private. Transaction fees are low enough to be viable for ¢ level payments. BTC is obviously the big one - but higher fees.

I don't know about your payment processor. There are open-source distributed Internet money payment processing platforms you can self-host, and integrate yourself into your site. E.g., BTCPayServer, MoneroPay (moneropay.eu) - I don't know how good those are. There are also service providers, like mixpay.me. Some of the big payment processors are starting to get into accepting some crypto payments - but usually heavily constrained by jurisdiction, which may make it less attractive for the payer even if it might be more convenient for the payee.