The most editorially interesting combo. Tea country, Buddhist ruins, hill stations, surf coast — then a 90-minute hop to the Maldives. Recommended length is roughly 6 nights in Sri Lanka, 5 in the Maldives.
Pacing
Land in Colombo, drive to Kandy or up into the hill country, then loop back down to the southern coast (Galle, Mirissa, or Tangalle) before returning to Colombo for the morning flight to Malé. The Maldives leg should feel like the rest after the Sri Lanka portion's pace — many travellers prefer Sri Lanka first, Maldives second, for that reason.
Booking notes
SriLankan Airlines' daily UL103 covers the Colombo-Malé leg cleanly. Book it as a separate ticket from any long-haul to Sri Lanka — gives you flexibility if your Sri Lanka itinerary shifts. Sri Lanka is a left-hand-drive country with workable roads; a private driver and vehicle is the standard arrangement for the inland portion. Get quotes from licensed operators rather than guessing at a fixed daily rate.