HTs are not ‘comfortable’ unless you have the right mindset. You have to accept them and ride them for what they are. Technique, position, standing etc.. Changing the material of the frame won’t change it from a 1 hour bike to a 5 hour bike.
Get the geometry you want, worry about anything else later.
Me, i’d be putting frame material below Bottom Bracket type and Headset type, they’d be more important to me.
I’m not sure frames themselves are necessarily poppy and jumpy, again that’s as much the rider as the frame to an extent. If you get a short chainstay 27.5 it will be more poppy than the long chainstay 29er like a Solaris of course.
Most of this is common sense, you’re not a daft lad by any means.
The Commencal Meta AM HT thing looks an absolute blast and is decent money. The Bird is hard to beat too.