If you're really in Zone 7 (the mountains, for the most part) you won't be able to keep Cistus through every winter. Figure on a ~15 degrees F. floor for these. I have seen the collection at the Seattle arboretum decimated by a hard winter.

The tall, ~hardy one here (Seattle area) is C. laurifolius. Quite a range of rock roses can be easily seen in local nurseries and gardens at the moment, as we have been having mild winters. If you want a comparatively reliable one, choose from C. x hybridus, C. laurifolius, maybe a few others.

I thought I'd give it a shot even though it's borderline here because our yard seems to be a microclimate within a microclimate. I haven't figured out why yet, but our south-facing front is always noticably warmer than everything else within a few miles, even more so than other south-facing properties in the area, and even in the winter (if it weren't a difficult slope I'd consider putting a vegetable garden there). We're stuck up on the side of a "mountain" in an area with no shade from firs or other large trees (most are below us), and the front yard soil will actually be warm while the back yard is frozen (where the ground is shaded by the house and surrounding fences). I know that air temperature can be a problem for the branches, but if these plants can take pruning of damaged tips, this might not be an issue. Also, there's a long, solid, 12' high hedge of arbor vitae in the direction of the winter prevailing winds (between us and the neighbors) so there are never cutting winds over that ground.

My front yard is a nightmare to plan for because the moderate temps in the winter are "balanced" by hellish conditions in the summer: air and soil temps well above the surrounding areas, with extremely dry, hot breezes. About the only thing I've found that does okay out there is lavender, and that's only with a decent amount of supplemental watering. I've worked out a plan for the front that includes all desert-native plants put into well-amended soil with excellent drainage (so their roots don't rot in the winter), but I'm having issues finding desert-natives (or the like) that can take the zone 7-ish winter temps. And if all of that weren't enough, I wanted as many as possible to be either fragrant or attractive to hummingbirds.

Okay, enough rationalization. I'm intrigued by the gummy resin, which I've been lead to believe (from a lot of online reading) is more prevalent -- or more potent -- in the ladanifer species. Is this incorrect? I may well have to learn the hard way that my front yard isn't as balmy and protected as I'd like to think, but I'm really more concerned with fragrance at this point. Humor me. Please. :-)

Other plants with gray or silvery leaves are likely to be compatible with lavender. Forget about amending. Buy some pit run and dump it on top of the existing soil, if it is too heavy, and plant in that. What district are you in?

Here is a link that might be useful: Washington USDA Zone Map

C ladanifer gets big. So does laurifolius. Both have a lovely resinous scent. In your zone I'd go with laurifolius, you have a better chance of keeping it alive. It's not shiny like C. ladanifer but still very nice.