I have no plans to get married or bring a chica home at the moment. I tend to keep my eyes open, but if the flow is pleasant, I go with the flow.
My observation is that the girls in the capital and places like Sosua and Pto Plata tend to be more mercenary than the chicas one meets in smaller towns. In 1986, I went to Barahona, arriving about 2:00 PM. I got a room and went out looking for something to eat and met a chica called Lorena, who gave me a psst! from where she was sitting in front of her house. We went to the movies that night, then went dancing and had a great time, and after that she showed me all around Barahona, we went to several beaches, all the usual puntos de inter?s and I had one of the best times of my life. I bought food, she made some really great sancocho, quipes, lambi. I am not all that fond of Dominican food in general, at least the stuff my Ex once used to make, which was always too starchy and greasy, but Lorena was a great cook. She and her mother had some sort of eatery outside of town.
She even gave me a tour of a local cathouse. I asked her why and she said "para que sepas". I said, "why would I want to go there since I have you?" and she gave me a 15 minute kiss, which sort of turned into a terrific tumble. I had planned to stay for three or four days, and instead spent two weeks.
I wrote her when I got home, but I never got a reply. As? es la vida.
Barahona is pretty hot in July, though. I live in Miami, which is hot, humid and flat. Ocoa is cooler, probably drier and mountainous, and the small town people are a lot friendlier.
I will look into the other places you mention. I was also thinking about Constanza, but the last time I tried to get there, there was some sort of landslide and they told me that bus would not be running a day or so. The Rough Guide mentions several adequate hotels. The Rough Guide to the DR (2011) mentions the Sagrato de Jesus and the Pension San Francisco and some place outside of town called Rancho San Francisco. I am sure that there are many others. I am not too picky about accommodations, functional plumbing, no bedbugs and doors that lock are pretty much all I require, and of course, some place that is chicafriendly., which tends to be everywhere that is fairly cheap.
I was in San Juan de la Magana in '88, I think. I had a fairly good time, but then it rained for several days and I never met anyone I really hit it off with.