Hi Mick
I recently went through a similar thing with my steampro. Having spoken to Prochem technical I have bought 2 x 25' extension hoses giving a total of 75' of hose. Prochem did tell me that you can go to 100' but then you will notice a loss of power so extra vacuum passes may be required.
The point about the hoses is correct so make sure you get the right solution hose. Whilst on the heater, if you have the heat N run from prochem then you will find it better when running long hoses to have the heater on the last connection to the wand instead of hanging from the machine otherwise you will lose heat over the distance.
With the extra hoses you will never be lugging your machine up stairs again! I typically only use 2 sets but have used 3 sets on three storey houses without any loss of power.
You can speak to prochem's technical support on this who I would hope will confirm what I have said. Prochem will also supply the hoses, albeit a little expensive. I got my hoses from Woodbridge Commercials Ltd 01279 422220 and saved about £70 on prochem's prices. I also got free velcro carry straps that I also use to lash the hoses to the banisters.
If you do use a third party supplier such as woodbridge be sure and tell them which machine it is for so that you can be sure you get the right connections.
Hope this helps
Chris