With regard to Flat or Convex mirrors, we had discussion on the forum a while ago and it's really up to personal preference.
Convex mirrors give a greater field of view, but the image will be distorted and everything appears further away than it is.
Flat mirrors make it easier to judge the distance of vehicles behind you, if you need to pull out to overtake.
We got ours from The Caravan Shop, Glasgow and they arrived to us in East Anglia in less than 24hrs. If you decide to buy some from your caravan dealer, they may allow you to try both types by sitting in their car park, so that you can see what the rear view is like with both types.