I am going to Sri Lanka in the beginning of April. I want to spend about a week on the beach, just taking sunbaths and swim near coast. I don't need any water sports. I want to find the place with still water without big waves. Which beaches in which parts of Sri Lanka I should choose. Different articles gives me a completely different information, and I am very confused.
The monsoon rains generally do not start until the end of May in that part of the world. What this means for you is that, the ocean on the western side of Sri Lanka is generally calm until June. So, I would say any beaches in and around Colombo or below would be great to check out.
As a bonus, you might be able to do some "blue whale" watching, if you go to the southern side of Sri Lanka (Trip advisor Link).