I certainly agree with MicSanToro about Ceylon Tea Trails. For us, it was hotel perfection. You have a choice which bungalow you fancy or you can divide your time between more than one of them. Getting there is a choice between an interesting if tiring road/train combo or a seaplane from Colombo Airport which can take you on to other places.

In Galle, I think Amangalla is the best option - we stayed nearby at the Galle Fort and while it had bags of character is also had a lot of weaknesses. A third of the price, though. For beaches we stayed at two places on the west coast, both of which deserve your consideration - Saman Villas and Calamansi Cove. Amazing beaches at both places.

I don't personally think Colombo warrants a long stay. I thought the newishly restored Galle Face was the best choice these days.