Adding cooling to 1990s Montana home – GreenBuildingAdvisor

Here is the scenario: My dad just bought a 1990s single family home in Montana, where he has never lived (nor have I). We are now in the process of updating the home, which has hydronic heating embedded into the slab on grade. I know that system may or may not be nearing the end of its life 30 years later, but the intention is to continue using that radiant floor system to heat the home. We now want to add cooling, as summers are getting hotter. The two-story house only has 8′ ceilings, and I am worried that the plenum is not large enough to introduce a ducted system without dropping soffits everywhere (I’d like to avoid this if at all possible). 

So, my thinking is to install radiant hydronic cooling in the ceilings, and switch out the boiler for some kind of equipment that can run both hot and cold water (I’m very new to construction so I don’t know all the correct terminology yet. Is this a heat pump? A chiller? Basically a reversible evaporator/compressor that can send hot water to the floor in winter and cold water to the ceiling in summer.) If this is possible, I would also need some way of getting fresh air into the home, possibly using an ERV. 

As I’m very new to this, I’m looking to get some expert on opinions on: 1. should we be abandoning the radiant floor heating all together? I believe the pipes are copper. 2. Would the need for an ERV or other fresh air ventilation system give me the same plenum/soffit problems as just ducting the space? Are there ways to bring in fresh air that are less space-intensive? and 3. Are there any other possible solutions for cooling the home that I’m missing? 

For reference, I do not want to install mini-splits because I think they are horribly ugly, and my main priority is a high indoor air quality and maintaining the ceiling clear height. 

Feel free to explain things like you are speaking to a ten year old, and thanks in advance for the advice!