Need opinions -- wool or cotton?

A close friend is getting married this fall.  As part of her wedding gift, I agreed to make the cover for her guest book. I have the concept planned out, but can't decide on the materials.  This is where I could use any/all help and opinions!!!!
 
She and her husband are, as my parents would say, "new hippies" -- very into organics, very green, ride their bikes to work, even here in DC, love to hike, vegetarians, etc.  I say that because if I were making this for my sister, it would be silk and fancy.  They are so NOT silky/fancy people.

They are going with the fall theme -- fall colors, centerpieces with little pumpkins on them, etc.

I was thinking that I would make the majority of the cover in a beige-y linen -- just like the side  background of this forum, actually.  I was going to applique leaves on one side, and a friend has offered to use their embroidery machine to do their names and the date.

Here is the big question -- what do I make the leaves out of? I was originally thinking shot cottons/moda cross weaves, because I think the effect would be pretty.  But is that too fancy for linen?  My other thought was wool felt, but I worry that it would be *too* informal.

I am open to switching to another background besides linen, but that feels pretty perfect for them.

Sorry this is so long... PLEASE share your thoughts!

I LOVE the Moda Shot cotton idea! I just saw the beautiful collection we have in the Sew,Mama,Sew! shop the other day. Here's a link to the selection we have: Shot Cotton

I would love to buy some of each color!

Embellishing the guest book with these will be amazing! I hope you share a photo with us when you are finished.