You have ten days for your holidays and you want to relax but also see something, but trouble too much with driving around the island and spend a lot of time in buses or cars. If you have just ten days and want to go to beach and relax but as well get a little culture and learn about Cuba, you should split the time and spend some days in Havana and the rest on a Cayo, or in Varadero. In this way you have both culture and beach.
Depending on your preferences I recommend: six days in Havana and 4 days in Varadero, or if you are more into lying on the beach the other way round.
For tips what to in Havana check the other posts or ask me directly.
The Viazul bus to Varadero just takes about 2-3 hours and costs about 12$.
If you want to take a taxi on your own it’s about 90$.
In Varadero there are a few BnBs, but they are booked out pretty fast, so if you want stay in a Casa Particular and not in an All inclusive Hotel, you should consider reserving in advance.
Or you could consider a few days in one of the hotels to relax completely.
Varadero is quite touristic and because of that more expensive than other places in Cuba.