I should get serious and take the risk with some HY pants. I guess its just I have 'athletic' legs, so I know for example Robs chinos wouldn't fit or suit me (...and went chino shopping a while back, and only one pair in about five fit, and ended up with some Tommy Hilfiger ones which are a classic fit/ not tapered too much etc). Same issue with jeans.
I'm sure the HY fit is a bit more 'traditional' anyway?
I don't have any HY trousers (although I'm seriously thinking about getting some), but I've heard that whilst they are slim, they aren't too slim. Furthermore, Jamison of HY stocks two, different cuts, an Italian-made cut and an American-made cut. The former is slimmer than the latter.
HY gives pretty good measurements for trousers on the website, including waist, thigh and knee measurements, so you should hopefully be able to compare the measurements to a pair of your existing trousers so as to get a pretty good idea as to whether they will fit or not.
When I was doing a lot of cycling, I used to often have to get trousers that were a size too big for me, so as to accommodate my thighs and backside, and have them taken in around the waist. However, my waist has now expanded and I just buy my natural waist size nowadays!