The Sidi Mega MTB shoes weren't quite right for me. I also had no luck finding cushy insoles to replace the thin Sidi insoles. I couldn't find insoles wide enough that still were reasonably the correct length.
I recently got Lake MX241 in Wide. The LBS only had the road shoe version of these, and I tried those on for fit. These fit exactly the same when they arrived.
I have foot joint problems, and not much padding under the foot, so Oboz hiking insoles worked great on these shoes. My riding comfort much better now, I wish I had gotten these a few years ago. These shoes are very expensive, but completely worth it to me. I got these slightly large, and wear thicker socks for better padding all around (and better in winter too.)
It's got to be difficult if you can't try the shoes on in advance.