Barbados is expensive but depends heavily on tourism so there are lots of tourist-type things to do. They go to great trouble to treat tourists well.
St Lucia and Grenada are less developed though both have some resort-type areas with lots of restaurants etc.
The southern end of Tobago has lots of affordable hotels, eating places, two nice beaches within walking distance and a couple of others not far away, but there's lots of unattractive development. The northern end and windward side are beautiful, lush and green, also with lovely beaches, but you need a car to get around.
Be aware that since they all depend heavily on tourism there's more crime than they are likely to warn you about, probably especially in Tobago. Service and attitudes to tourists in Tobago can be sadly disappointing, too.