Spirit Airways sells the massive Front Seat onboard its plane, which is analogous towards the seats in US domestic first class, but there's no other variation in services or features for purchasers seated in that segment. However, booking these lovely suites to and from the U.S. is nearly not possible: https://businessflightshop.co.uk/blog/why-do-airlines-overbook-and-what-should-you-do-then/