Need help on choosing health insurance company

I live in the UK and will be sending my son away in a few week to start a four year football scholarship in the USA. As you can imagine we have healthcare provided in the UK and the thought of handing my sons health over to insurance companies fills me with fear. Can any of you help advise me which companies provide the care without fuss? He is a fit and healthy 18 year old but I know companies look into your past to find a way of denying the care you need in some cases. Would really appreciate some advice from the people who use the system. Can anyone help!