Try Samui Villas website....and the Sandalwood Villas are highly recommended by TripAdvisor. Just remember that if you choose a villa that's a bit off the beaten track you will have real issues getting to a main road when it rains! And some of those villas are up very steep drives.
Avoid Chaweng..it's horrid......came back from there a few weeks ago..had a great holiday as was with friends but the town has become really grotty and dirty. Best to stay near Fishermans Village if you want some decent restaurants and pubs.
This is terrible, we went to Koh Samui for our honeymoon nearly 21 years ago and I *think* we went here:
http://www.tongsaibay.co.th/en/04-services-facilities/03-activitie/index.php
though it's changed a bit since then..
Otherwise, I think I'd choose this if we were going now:
http://www.abercrombiekent.co.uk/thailand/kohsamui/library.cfm
(To situate ourselves, we were lucky enough to stay at the Oriental in Bangkok and in a similar quality place on Koh Samui, due to staff discount!)