I want to go an see a medium to contact my mum and I would like reassurance that she is ok now. I don't know of anybody however, how would i find a good medium.?
Find out where your local spiritualist church is and go and see what they say there. Who knows something might happen for you there, if not no doubt they will know of mediums they think are good.
The understanding of a 'good' medium can only be based on personal experience and your own view point, so you will probably only really know how good they are (to you) after the session.
dont go to anyone that will charge you for their services. Your local spiritualist group will help. My local one has meduims in every Sunday that will only take a donation if you are satisfied with what you here. Look in local paper for any group meetings.