The healthiest alternative to get around Koh Samui is renting a bicycle. You can choose to take a guided tour around the island on bicycle or just explore by yourself. Either way, you must keep a few things in mind before deciding to rent a bicycle:

the temperatures during the day are hot hot hot. Make sure to wear sun protection and bring water with you
don’t underestimate the traffic
if you’re planning on visiting remote areas, inside the island, keep in mind that it will take a lot of effort since the roads are very steep
Price
A good mountain bike will cost you around 80 baht per day.