Siboya is a medium sized island south of Krabi - just to the north and closer to the mainland than Ko Jum
I rate it equal in "untouristy" to Kos Sukorn, Libong and Yao Yai. Main activities are cash cropping and fishing. The 3 resorts on the west coast have minimal impact.
I picked Siboya Bungalows, the first resort to open. It is situated on a long flat area behind the beach. This area is about 100m wide to where it merges into a low slope towards the coastal road. Most of the 20 bungalows and the private houses at the resort are situated on the flat. There are extensive lawn areas around the bungalows and manicured gardens around the private houses. Many of these are for rent when the owners aren’t holidaying at what seems very reasonable prices.
House owners are largely old-time Thailand hands who holidayed with resort operator Mr Chung back in the day when he ran successful places on Phra Nang and Railay. So successful the leaseholders kept increasing the rent and forcing a move. Eventually he decided on finding the best building site on an untouristy island and quite a few of the Farang regulars threw in money to help the purchase - and later built their holiday houses. Some winter here for 4-6 months. You always get a warm greeting from them when arriving at the restaurant - and this seems to spread to short-time guests.
Mr Chung runs a class act - the food is great at about average budget bungalow price, the bungalows and grounds are spotless and he is the perfect host - remembers your name and quietly asks every now and then if everything is okay.
My 250 baht bungalow was rustic, very close to needing some TLC with timber renewal. Just enough room for 2 and their gear. Clean. Thin but comfy double mattress, ditto pillows. Mozzie net in good condition. Big indoor-outdoor concrete and tile bathroom, twin mirrors. No wash basin. Squat toilet. Toilet paper supplied. No longtail or traffic noise at night. Spacious verandah with nice outlook over big manicured lawn area to Ko Jum in background. The 350 bungalows were closer to the "beach", bigger and seemed newer. Great sunsets from bungalow verandas and restaurant.
Siboya is not an island for great beaches. There is a kind of starter-mangrove set-up directly out from Siboya Bungalow's restaurant. Low tide underfoot is dark sand and rock, not mud. At high tide there is a nice enough strip of sand a few meters wide along the beachfront and the occasional mangrove emerging from the water. About 300m north (and south) of Siboya Bungalows the beach improves, but it still aint Phra Nang.
Some posters have said THAI WEST resort has a better beach. I walked 10-15 minutes north and yep, it is better than directly in front of Siboya, but no better than immediately north-south. Nice looking resort BTW - but it seemed deserted in what was early shoulder season (mid-Nov).
Look I'm a beach junky, but knowing what to expect, I was not the least fazed. Combine your stay with a few days on nearby Jum to get your beach-fix.
I hired a bike and explored the rest of the island. Ban Siboya is the main village, but is pretty basic - a few stores and restaurants - no ATMs, money changers, computer shops. Most roads are dirt, thru flat and lowly undulating countryside with rubber plantations, cash-cropping and rainforest.
Access is by public longtail taxi from the mainland after a songthaew trip from Krabi. Google Siboya Bungalows for details.
Lot of thanks for valuable information! If not this info, I would head to Koh Siboya with high anticipation of the beaches like on Koh Jum, then Tezza's Koh Siboya beach inspection report has helped me to amend timely the itinerary.