I've never tried the Humanity or the SnugTuck, but I can say that I LOVE the Tres Tria. I didn't know what to expect when I first ordered it, but it's turned out to be an incredible purchase.
First, the natural latex actually stays amazing cool. Way way cooler than any other bedding I've ever had tried. My latex pillow is the only one I use on really hot nights, it almost has this squishy minty-ness to it. Sorry that sounds weird, I really don't know how to describe it! =) But I love using the Tres Tria as a body pillow too.
Second, the baby won't actually sleep ON the Tres Tria, as far as I know. It's more of a divider/bumper to keep kids from rolling off the bed. And it really does work - when you stick it under your sheet, it becomes immobile.
Third, both Organic Grace and Better for Babies have wonderful service. I couldn't give them higher reviews! I think Leah at BfB actually designed it, so I'm sure she could answer any questions you have, and maybe could recommend something for your situation?