A formal shirt that's not a sensory nightmare???

Hi, 

Does anyone have any recommendations where in the UK to buy a button-down white business/formal shirt that's comfortable for someone with sensory issues to wear? I can stand most casual shirt fabrics, just not the type usually found in formal wear - e.g. thick cotton, stiff starchy collars, etc. I expect something very lightweight would do. I also have the problem of having quite a broad chest, so shirts often come up short on the arms. So, I also need a longer sleeve to reach beyond the cuff of a suit.

I've looked everywhere, but nothing fits the bill. Any advice is welcome!