Suggestions for quick trip during Tet?

Quite unexpectedly, I have an opportunity to visit Vietnam from Feb. 17 - 26. I have to be in Ho Chi Minh for work on the 25th and 26th, will probably also spend the 23rd and 24th there too. For the rest of the time I am looking to see a bit of the country (maybe just Hoi An) and then spend a few days at a quiet beach with decent surf (for splashing around in, not surfing). I am thinking of flying into Danang (for Hoi An) and then hitting a beach on my way to HCMC - or, I could hit a beach around Hoi An, but I am led to believe that the surf there in Feb. is a bit dangerous.

I am wondering if people have any advice on where to go? I have travelled extensively through Thailand, Cambodia and Laos - but never Vietnam. My favorite places for relaxing in the past (and this was about 7 years ago) were the end of the road places in Ko Lanta and Ocheteaul Beach in Sihanoukville. Not looking to party up - just a laid-back, clean and inexpensive place to relax on a beach with some waves, read a book and eat some good food. Also open to suggestions about non beach places I shouldn't miss - assuming i can fit them into such a short visit. A possible complication is that this will be during Tet, which could complicate finding a quiet place and getting around.

Any advice will be greatly appreciated. Thanks.