no other critters need to be housed with your geckos. they must be in a cage all by themselves. for many reasons... climate, humidity, stress would be caused by the presence of another animal, they could be eaten, and geckos can be effected by parasites carried by other animals (this could be deadly!).
alot of us here at this forum have the desires for different species of animals, just look at our profiles/signatures! but we have to do what is best for our animals. that means housing them seperately. i love collared lizards, but i am out of room for cages. so i decided on leos rather than collareds.
as for the substrate dilema....... like you, i didn't want to give up my naturalistic cage. i knew i had to give that up for the good of my geckos. basically i decided i needed to give up my own selfish desires and be responsible to my geckos. for me, the final and most important reason that led me to give up on sand was keeping my tank clean and parasite/disease free. it just made sense that tile would be easier to keep clean and disinfected. tile would not harbor bacteria, parasites, germs and whatever else could harm my geckos! i hated the idea of paper towels, that is about as far away from a natural looking environment that you can get! so i was really excited when the idea of tile came to be, afterall, it is more natural in appearance that paper towels!
i apologize if i sound like i am on my soap box!
check out the pic of my tank below. try to keep an open mind regarding tile, even if you have to give up a little. i am really glad i did!

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Life, Liberty, and the Pursuit of Lizards
1.4.0 leopard geckos - raine, mango, noodle, jaws, & sobe
0.1 bearded dragon - sydney
0.1 king snake & 0.2.3 corn snakes
1 red eye tree frogs, 3 green tree frogs, 2 firebelly toads
5 anoles,8.0 bettas & numerous tropicals
1.2 dogs (dachshund-pepper, brittany spaniel-jenni, lab-kaci)
1 hubby & 2 boys
www.skayart.com