I'm a freelance writer and yogi living in Tepoztlan, Mexico where I'm running www.casadelcorazon.mx with my girlfriend. You can keep up with my other writing on www.bollocks2thewellingtons.com/
La Mer on Moon Muan Soi 6 is more of a hotel than a hostel if truth be told, but price-wise it's fairly reasonable if you're looking for something a bit above back-packer level.
It is associated with the Eurana Boutique Hotel just behind and you can tell it is a poor neighbour because they use all the old linen and towels from their big brother. On the plus side it means you can go and use the nice swimming pool next door for 100Baht and there is always a security guard in attendance in case you lose your key and get back after the reception closes at 10pm.
The rooms are nice, air-con as standard and when I was first here in the heat of summer that was very helpful. The beds are comfy and the showers hot, although the housekeeping is amusingly inconsistent... what will they forget to bring today?
Wi-fi is ok, although they introduced a new system requiring a log in each time which is a pain, to be honest. They have a TV in the room as well if you need that to keep you entertained.
I liked the place, the staff were generally friendly and although the restaurant area lacks character I was happy to stay here for a couple of weeks. Any longer and there are better options, and if you're on more of a budget then there are better options also.