If you are looking for quality sofas, there is no greater selection than at the Ilumel store. They have several floors full of sofas (and other furniture) of every design you can imagine and those you didn't know exist. They claim to be the largest furniture store in Latin America and by looking at the place that's very believable. Prices might not be as relaxing as the sofas themselves, but you said quality so... Many are imported from Europe, North America, and of course China/Vietnam.
The store is on ave Lincoln in Piantini. They deliver everywhere in the DR.
If you have expanded pockets, then go with the above.
For excellent quality and workmanship with reasonable prices, take a trip to Duarte Hwy, past La Vega and right before Moca. Full of stores and furniture shops. They'll customize and make anything for you.
Thank me later.