So here is the situation:

I live in a 1920 2 story home in Denver. It currently has a newer forced air furnace. Our existing duct situation is similar to what you might find from the old gravity furnaces. couple main baseboard registers toward the center of the house on each floor, and an extra branch toward the front of the house that serves the foyer and one upstairs bedroom. couple returns in the main floor. the challenge is primarily cooling the upstairs where the 3 bedrooms are...it gets pretty toasty up there.

We currently have a breezeair evaporative "swamp" cooler on the roof that works well for much of the cooling season and many nights in May, June, September when we can run it on just fan mode to cool the house at night with cool outdoor night air. This does wreck my allergies in spring though. Anyway, We try to get it cool and then close the house up during the day and pull the drapes. That doesn't work as well from mid-june thru august. Nights in denver seem to be getting warmer and more humid these days. Often the swamp cooler pushes the humidity up into the 60s in the house even on vent mode, which is just too damp. I dont want to get things molded or cause walls and floors to crack so sometimes we just sweat rather than add too much humidity. The other thing is that we have nice newer casement crank out aluminum clad, wood interior Marvin Windows...so I stress a lot about leaving them cracked all the time due to rain when the cooler is on. These casements also make window AC units impossible. The cooler is also a pain to start up and shut down each year on our steep 2 story and fewer companies seem willing to come do it. It broke recently and took it a week to find somebody who could even go up as my normal person wasn't available.

We also run the furnace fan about 15 min per hour to try and distribute some air during the day. With this current protocol, on hot days we might start out in the morning around 69-72 depending on the overnight temps. As day goes on main floor will creep toward 76 degrees, but the upstairs is more like 81-82. not horrendous for a house with NO AC. this is much improved with our newer windows, and improved attic insulation and ventilation....couple years ago it could creep into mid 80s pretty easily up there.

So getting to my dilemma...I would like to had some form of air conditioning. If this is reasonably successful I may eventually have the cooler removed and perhaps have a whole house fan put in that spot in the upstairs hall cieling since half the time we seem to only be able to run cooler on fan mode anyway. but I would probably keep the cooler for a couple years to see how it works out.

I have had 2 contractors come out.

Contractor 1: recommends adding central AC and to expect "some" temp differential between up and downstairs. Each bedroom has one register at the baseboard and I cant say the airflow ever feels terribly strong. you know its there but its not really a breeze. No air returns on the upstairs returns either. I know this is generally a recipe for a cold main floor and a still hot upstairs.

Pros: cheaper, probably make main floor quite comfortable, no ugly box on the wall, probably more acceptable for resale

Cons: possibly make it too hot upstairs still , the furnace fan is quiet loud.

Contractor 2: says there is something weird about my crawlspace and basement finishing that makes it not easy to get the lines from the outside unit to the basement furnace...he quoted 2 minisplits upstairs for about 2 grand more than adding the Central unit. not sure if he just makes more on it and doesn't want to mess with my tight crawlspace or if its actually a better solution. also not sure why he wouldnt do 3 heads, one in each bedroom

pro: get my bedroom really cold which I like,

con: probably wouldn't do much for the rest of the house although some of the cold air would maybe fall downstairs and make it less hot. Also not pretty, and probably not quiet either

Right now if I can manage to keep the upstairs within 5 degrees of the main floor with closed windows and drapes, fan running on and off, etc. in theory I would think this should all bode well for central AC. I guess that whats I am leaning toward. I am thinking that most realtors and people would generally prefer the forced air central. If I could keep the main floor around 70 and upstairs in the ~75 I would consider this success for central. perhaps closing the basement vents and running the fan continuous would even help with that too. my worry with Central AC that it might just worsen the temp differential though and make it like 70 downstairs and 80 upstairs.

Given all this tedious detail would you err on the side of Central and accept some inevitable upstairs/downstairs differential in temperature? or go with mini splits? Any things I could think to do if I add central that might help upstairs like duct booster fans?