How to Rank for Multiple Keywords

I currently rank #1 for my main kw and I am in top 5 position for several other kws of note. My root domain is ranked for all of these kws.

I would now like to go after several other kws but my feel my root domain is saturated. I do not see how I could effectively optimize my main domain for more kws w/o affecting the ranking for my current kws.

Following are my options as I see it:

Option1: I could start actively building quality, anchor text back links to relevant content on my blog which would produce indirect traffic to my ecommerce site. I am not too fond of this idea as it places an extra step b/w my ecommerce site and my potential customers.

Option 2: I could build quality, anchor text back links to relevant internal pages of my ecommerce site. A reasonable option but my main concern is that as an ecommerce site, my internal pages are always changing.

Option 3: Create mirror images of my root domain. These would be mirror images in a structural sense but each mirror would have unique content specific to the chosen keyword.

These pages would be something like this:

www.domainname/keyword1 (page would have unique content and would be fully optimized to target this KW)

www.domainname/keyword2 (page would have unique content and would be fully optimized to target this KW)

etc...

I am leaning toward option 3 but would like to get opinions before moving forward.

Thanks...