I have never tried Bolivian food, either, but I am definitely looking forward to visiting Bolivia over Navidad and trying out some of the great food and learning some tips from the suegra! My boyfriend is from La Paz and has lived here 12 years, so I asked him for some tips on finding Bolivian food in Buenos Aires.
He points out that wherever you go, it will not be the same because the ingredients don´t have the exact same flavors as Bolivia, so wherever you go, even a Bolivian restaurant, will just be a re-creation.
Barrio Bajo Flores has a huge number of Bolivian immigrants, so Flores is a great place to go for lunch. But Flores can be not a very lindo lugar at night. He pointed out that a lot of the Bolivian restaurants are run by Bolivians and are good as in have good food but are not big on ambiente, as in atmosphere. They are a far cry from the trendy places in Palermo Soho. You might not find any English speakers there because these places are Bolivian food places made for Bolivian people, not catering to tourists, but it sounds like you are up for just such a place!
He knows of a decent place in Flores at the intersection of San Pedrito and Alberdi (which would be Alberdi somewhere between 2800 and 2700-ask any verdulero, a person working at a vegetable store, where the Bolivian restaurant is there) that he thinks might be called Pancitos based on a web search (he says that one is a little more upscale in terms of the atmosphere if it´s still around) as well as one we found on the BA tourism website in Flores called Penélope at Avenida Nazca 55. I also found onlye a restaurant called "Illimani" in Liniers neighborhood (which is the mountain right next to La Paz) address Rivadavia 10960 and "La Paceña" in the Belgrano neighborhood, address Echeverria 2570.
Warning: these are places I have not tried myself but found on the web and from talking with the beau.
Good luck! I may be venturing right behind you soon.
Emily