Measuring well-being – can children's measures be adapted for vulnerable adults?

I'm doing an SROI audit on an organisation that provides services for people with learning disabilities.I would like to be able to say how this affects the quality of life of people who are supported, and therefore I need repeatable and robust measures to do so.
The key difference between what this organisation offers, and what is typically used, is the typical audits measure the tangible things (how often do staff could appraisals, how many staff, is there a fire and safety plan in place), whereas this service finds out from the users themselves how they feel about the service given.
I had a look atsome of the ways of measuring personal well-being, for example, some of the self reported measures. In the course of this research, I had a look at some measures used with children: they are particularly interesting, because one of the examples given ("how do you feel about your autonomy?" Translates into "do you feel you can make your own decisions?") just shows how far we are from using clear language with adults!
For those who want to find it, here is the report by the highly esteemed new economics foundation.http://neweconomics.org/publications/guide-measuring-children%E2%80%99s-well-being