Solid Hardwood, Engineered and Laminate Flooring - Subflooring under old floor

I have decided to refinish the old douglas fir T&G flooring I have throughout much of my house. The part of the house I am redoing was built between 1930-1950. I pulled up the carpet to expose the floors and found them to be in good condition. They have never been resanded that we can tell and have been covered by carpet for a little over 30 years. One board needed repairing and in examining it I found that the flooring is nailed directly to the floor joists... no subfloor. I would really like to refinish these floors but living in Colorado, the lack of "insulation" would probably be a problem. I figure any gaps would produce a very noticeable draft.
So my question: Is it worth pulling the old boards up (numbering as I go along), laying down a subfloor (exterior plywood?), and then relaying the boards on top? I have also been wanting to get into the crawl space to put in some floor jacks under the joist for a little additional support (the house sits on dry, unmortared rock). Pulling the boards up would give me access to joists that are too close to the ground to access from below. Proverbial two birds with one stone.
My skill level: land surveyor who is handy around the house, hates plumbing, does electrical, and does not do as well with very detail type jobs due to lack of patience. (i.e. a better framer than cabinet maker).
Scope: Right now I am only in one bedroom but whatever I decide will then entail a repeat in the living room. Those floors would look so GREAT once finished.
Thanks for your help and advise.
Teresa