You can't go wrong with Levi's for looking like a regular guy. Not the cheapest, though. There are multiple styles: tight, relaxed, boot-cut, etc. For wearing with your cowboy boots, go for the boot cut.
You will need your inseam measurement. Men's jeans are sold with two numbers on then, like: 32x30. The first number (32) is the waist measurement. The second number (30) is the inseam measurement for leg length. You will want to try them on the first time you buy them, just to check your measurements against the manufacturer's standard.
Once you know what your measurements are, they are a much more realiable indicator of size than the size numbers on women's clothes. Men will think nothing of going into a store, picking a pair of 40x32s off the shelf and heading straight to the cashier, confident that they will fit. Except when their beer gut has grown, of course.
