No idea of your budget but your best bet would be to do a hotel search in District 1 (often referred to as the backpacker area).
I stayed on a street in Saigon which, from memory, was called Bien Vue. It cost around USD 50 but I was treating myself to an upgraded room and this was by a wide margin the most I h ave yet paid in 6 weeks in Vietnam and Cambodia. There are lots of much cheaper hotels on the same street and other nearby ones.
I also stayed in the Old Quarter in Hanoi and the two areas are very similar: Lots of cheap restaurants and bars all around so plenty of scope to meet people, tourists or locals.
Good luck with the search.