G,Day and welcome Jutta..
Thinking while a 9' soft floor should be reasonable easy to handle, it might leave you a bit crowded with little floor space, by the time you put a couple of bunks and a small single stretcher in there .
Our old camper had an 8' x 7' floor space and with two stretchers, It didnt leave much space, but for us it was comfortable enough for two week trips [ even with 5 odd days of wet weather ] and would have worked for us on extended trips ...
It realy depends on how little or more gear you need to take and how good you are at organising it, If you are able it might pay to get along to sales yard / show or hire a few different campers to get a better feel of what space you need .