I just came back from a short break to Koh Lipe which is situated off of Thailands West coast.
The island itself is stunning and only approximately 1km long by 0.5km wide. There are three main beaches on the island, Pattaya Beach (the main beach), Sunrise Beach and Sunset Beach.
Pattaya Beach
Sunset Beach
Sunrise Beach
There aren't any paths that go around the outside of the island but instead the inside of the island is criss-crossed with concrete paths. The only way of reaching all of the beaches is to either walk using the main access routes, take a taxi boat for THB50 or hire a kayak for the day. I was there at the very end of peak season (November to April) so the island wasn't too crowded.
I'm always keen to explore so after looking at the existing access routes, I walked to the far western end of Pattaya Beach and went inland, crossing to the other side of the island close to Hoy Passan Hotel.
There was a small beach the for the resort but I found that turning left, you could go past the rocks by walking in the water which had a smooth sandy bottom and only came up to about knee height at the shore. On that side there are several small sheltered and private small sandy areas which are perfect for nude sunbathing and also swimming. I was there with friends so I couldn't stay too long but I managed to enjoy some nude time for about an hour.
I should add that public nudity in Thailand is illegal and even topless sunbathing is frowned upon, although I did see one topless girl on Sunrise Beach. Also the swimwear of choice for girls seemed to be thongs as most of the crowd are young Western travelers. But nude sunbathing is possible if you manage to find a quiet, secluded area to yourself! My impression is if you find somewhere that is difficult to reach, most people won't bother and you should be ok! Just beware of the kayakers