The difference between mesh and non-mesh is mainly if you use it also in winter. Because if you put the backpack on snow (or fall while skiing) and snow gets between mesh and back - you won't clean it easily. I had exactly the same dilemma a few weeks ago (especially since wife swears by mesh, all my backpacks so far without) - tried both. The one with mesh (GREGORY Zulu 35) really fit the back panel like poured, without mesh I tried GREGORY Stout 35. Honestly, with Stout I had to fiddle more to set it properly (has adjustable back, men's backpack - differently shaped shoulder straps ...). Decided for Stout and tested it a good week ago from Matizovec to Kofce (loaded about 15kg stuff inside). When set properly, you carry it with hips and it nicely distances from back, so when we arrived up I was almost not sweaty on the back, nothing on shoulders either. Has space for 3l bladder, two mesh side pockets, front pocket for quick stuff, rain cover, top outer and inner pocket, very thoughtful closing system - with one hand even with gloves on, loop and strap for thumbs/ice axe, pockets on waist belts. And can open from bottom too. If you like to carry extra mat for wife to sit warm and soft, has straps below. Bought it at
https://firstcornershop.com/sl/izdelek/gregory-stout-35-nahrbtnik/ ... they have big selection. They have at the end of February an action where 15% from each sold backpack goes to Slovenian mountain guides association.
You can contact me, I'll tell you more. Backpack excellently presented on video
https://www.youtube.com/watch?v=vSNvGqQhMY4&feature=emb_logo