I have a Tatonka "Bike n Hike" backpack that I use as my daypack. It has a trampoline back and there is no way I would go back to a non-trampoline back. This particular pack is well designed and the gap between the trampoline and the pack itself is quite slim, just enough to get your hand between them (which BTW is a great place to store my Bora hat when not walking). Also, inside the pack is very straight as the small gap allows it to follow the line of the metal stays which are only slightly bent.

A couple of weeks back we hiked in the Royal National Park in 33C (92F) temps with a hot, dry northwester and except for the hip belt my back was dry. As someone who sweats on the top half of my body the dryness was welcomed.

The trampoline doesn't stop sweating it just provides access for air to circulate and cool/dry your back. Ultimately you need to go to a decent outdoor shop and try some on and then decide which one you like.

Cheers,
Michael.