Couldn't really think how to title this question which is probably why my google search and Ebay hunt was unsuccessful!!! - not too sure of the correct name for what I'm looking for so please bear with me. Have a couple of very large squashy sofas - the cushions I sit on and lean against are very deep but don't support my back at all - I don't particularly want to replace the sofas and would like to 'firm them up ' somehow -There must be something I can use - the cushions I sit on and the ones I lean against are quite large - almost like bolsters. Many thanks in advance for any advice.