I really like the idea of layering rugs with a pretty rug on top of something much bigger and neutral like a sisal. The only reason I didn't suggest it earlier is that I thought the reason for looking at smaller rugs was to allow more hardwood floor to show around the edges. If we're okay covering the wood floors (which I am), then definitely, let's look at big neutralish rugs.
And I like sisal, but, I don't like real sisal because it doesn't feel so soft or good on my feets and I think sisal hates moisture (which is probably not a big issue). But I do like synthetic sisal plenty. Here are just a few quickly collected examples -- there are lots more out there.