The first thing to say about the Beach Boutique House, is that it is infact part of a much larger complex called the Beach Heights Resort. Secondly its not in Karon Beach, as the address states but in fact in Kata beach. All of these factors can make it tricky for drivers to find initially.
While the Beach Boutique House is right at the back of the complex it does make it nice & quiet away from both construction & traffic noise. The rooms surround a series of pools of different depths.
The room is tidy & functional. There is a 10 minute walk to the beach, via a decidedly smelly waterway, but Kata Beach itself is lovely. We preferred it greatly to the larger Karon beach, which is also within walking distance, 20-30 mins, though the smaller Kata Noi Beach, at the far end of Kata, is also worth visiting.
In short the Beach Boutique House is not amazing in terms of service or quality but it is in a good position & fulfils your requirements.