I don't have a treatment couch either - wow, Stampy, you lug that around with you? My back couldn't handle that!!
I've been working mobile for a year, and my pedicures are one of my most popular services.
* I have my client sit on a comfy seat (either a soft chair or sofa), and I have a small waterproof sheet that I place under my footspa to protect the floor. I have all my towels, lotions and nail kit at my reach so I don't have to keep getting up and down.
* I find it easier to sit on the floor crosslegged, but you can use a small stool (there's a great little blue fold-up stool for sale in Asda for about £5 - I see the ads for it on telly all the time *put "folding blue stool" into ebay, and you'll see what I'm talking about)
* I use plastic poly bags as liners for my footspa (although the footspa is sanitised between each use, this is an extra line of protection - also, my footspa has no internal jets, so the water doesn't contaminate the inner workings)
* I use the top of the footspa to rest my client's feet when I'm doing cuticle work, or when polishing. It adds a few inches in height so my back doesn't strain and is still very comfortable for them.
I have a portable nail table that I use for most clients, although for repeat clients I soon learn which ones have space for it (some places don't have any room for one!) Also, sometime clients have a table all prepped for you in advance (the waterproof sheet helps to protect against any spills, though!). I've never worried about carrying my own chair around because 1) I've got enough to carry! and 2) I'm only sitting on it for 1-2 hours, so it's not like I'm spending 8 hours a day, 5 days a week on an uncomfortable seat. That being said, I have yet to find a seat THAT uncomfortable at a client's house!!
Good luck, and don't be nervous - you'll do fine!!
Dawn