I bought the Alpinestars Bionic 2 body armour and find it excellent. The main problem as you point out is the size of the elbow guards which I could just force into my Frank Thomas X terrain jacket in Large (L) without the cold weather lining in. Decided to go up a size and spent some time in Hein Gericke trying on the Touareg with the armour underneath. The store were helpful and the manager spent ages removing the fitted stuff for me. Result was that I needed to go up one size from L to XL. Unfortunately they didn't have the non Gore-Tex in stock and no way could I afford the expensive stuff, plus I needed the kit for that weekend.
Next stop was Mark Philips just outside Lincoln. (
http://www.mpmcc.co.uk/). Sorry no where near Reading

But what a great place. Really friendly and helpful with more stock than you can shake a stick at. Tried the Akito Desert without the Bionic underneath and found I needed to go for XL rather than L, one size bigger than FT or HG. With the Bionic underneath I found that XXL was a better fit (2 sizes up). Once again the staff were keen to get the right fit and happily dismantled at least 3 different sets of jackets and trousers of armour and lining to make sure of the fit in all weathers. Purchased desert jacket and trousers from Mark and am happy with them so far, especially for the price. As for service I couldn't get better. All in all I spent almost 2 hours dismantling and trying on and nothing but encouragement and help from the staff.
With Akito I found the standard sizing a little small in the first place. You may want to consider 2 sizes above.