Hello Ian,
My wife thought I should respond to this, partly due to the stete of my back, partly due to my experience in remedial therapy.
I have the 135 model, but it has the dry solvent system, built in, making it pretty heavy and normally I left it outside, using up to 100 ft of hoses when necessary.
This enabled me to work 2 levels up and by attaching the inline heater at the join closest to the tools I got exceptional results and am teaching my son to follow suit.
In spite of my back I was able to take the machine up the occasional flight of stairs, without mishap, but you must have footwear, which is non slip and use common sense when pulling up / easing down stairs.
Using body mechanics, and avoiding jerky movements anyone of average fitness / strength should have no problems.
The obvious alternative, is to have a lightweight extraction machine for difficult access jobs, we have used the little Karchers for years and in spite of rubbish tools, they have earned a lot of money.
Best wishes
rob m