I'd give working a try. I think you're on "income support" and they have different "employment support" which, as you say, will be less if you make a certain amount but probably won't be less overall to the income support you get now? If it all doesn't work out, you can go back on the income support. I'd rather try and gradually work my way up and healthier than lose my chances by remaining in part-time volunteer, shelving? There's no possible future there.