I’ve not been to the Amalfi coast, so can’t comment on that – if you’re looking to go with a tour company maybe they are the best people to talk to – and be clear about what ‘not very mobile’ means.
If your worries are about being on your own – you need to decide if you’re a tour group person (with all the planning done for you) or if you want to sort it all yourself. Anything is possible if you put your mind to it – but you need a ‘can do’ approach to it. Of course you need to be realistic, but I hope you won’t let worries about being on your own get in the way. You can do it!!