We went to Sri Lanka last year and the Maldives several years before. We did them separately, but they could certainly be combined.
For a TA, we used Red Dot, which is the same company as Sri Lanka in Style. I think most agents would go through those destination management companies (DSM) if they are US based, especially if they use Virtuoso suppliers. The DSM gets your tour guides at places like the cultural triangle, oversees the trip while there (i.e. checking in with the driver), and ensures that you have a great driver. All of those were true for us. Otherwise, you're just booking hotels and you'll find the most knowledge of specific hotels on this forum.
Ideally, a combo of taking some planes and a private driver through a DSM would be the best way to travel. We just used a driver but could have shaved off some time with a few internal flights.