When it comes to shirts, I have a real weakness for Joe Browns colourful offerings.
Sometimes I can get them on Jacamo, but for choice and time saving I invariably head to joebrowns.co.uk.
Sizes range from Small to XX large, which works for me, and although on the expensive side they are not outlandishly so. The shirts are generally true to their size, possibly a little on the baggier side, so it may be worth ordering a size down if you like your clothing with a snug feel and fit.