I also agree with OM. Unless you make the bag yourself, or can find someone to custom build it, you're going to be choosing between a short, medium, or long bag. Each will give a height range; just choose the one that is taller than you are. For example, I'm 5'10", so my choices are usually short ("fits to 5 feet 8 inches"), regular ("fits to 6 feet"), and long ("fits to 6 feet 6 inches.")

I choose the regular, even though it's about 2 inches too long. If I chose the shorter bag, my feet would press against the bottom of the bag, compressing the down there so it's not insulating my feet. In the regular, I've got plenty of length, and I've never noticed the "extra space to heat up" to be a significant problem (or even noticeable.) Some people I've camped with do get cold feet; they simply stuff a down vest, wool shirt, etc., to fill up the excess space, and the problem is solved. I used to carry down booties when it got really cold, which worked very well.

I don't know what conditions you'll camp in, but you might consider a quilt - essentially a sleeping bag without the hood or the underside. Without the hood, you don't have any real issues with the foot; you just put it loosely around your feet. Length is only an issue to the extent that you want your shoulders covered; if it's too long, just tuck the excess around your shoulders. You can extend the temperature range of the bag by also sleeping in a hooded down jacket and down pants (and down booties, if your feet are cold.)