Hi
Many older homes have a small hatch cut into a closet ceiling or an opening on the end of the house acessed from a ladder. Find a way,it will be worth it.
One '60s house had copper pipe in the poured floor. It worked fine except the insulation was nor up to snuff and the floors were too warm. Today the cost of copper will kill the job.
There are comanies that do spray foam insulation. This works well because the small openings that allow air to infiltrate into the house are sealed.
Dennis
My 30's farm house was uninsulated until last September. I had icynene foam sprayed in the attic, walls, and inside the sill. No more drafts, and the comfort is radically better. The house is TOTALLY different and now I'm ready to go for hydronic. I have a guy coming in to help me design the system, which will be installed with Pex snapped into aluminum fins under the floor joists. I highly recommend the spray foam route.