Best advice is to diversify. Why restrict yourself to carpets and upholstery when there are a multitude of services which need cleaning. Not much different just slightly different kit and processes but plenty of help on here and elswhere if you want to try your hand at owt.
Obvious one is drives and patios, ready made customers from your carpet cleaning jobs. Hard floors, again in the same homes or better still in commercial premises, these jobs can run into thousands of pounds.
Facias, petrol stations, drive throughs, stables, kennels, catteries, kitchens, windows, conservatories, air conditioning ducting, drains, picnic sites, toilet blocks, deep cleans in pubs, how many times have you stuck to the bar? the list goes on and on.