Consider a steel frame. My Blue Pig X (daft name, great frame) currently has a little 2.0 Mud XR @ 28psi on the back at the moment and is very comfy. There's some clever business done to the stays to make them compliant while the front triangle is stiff to give the best of both.
It's slack and I've got 150mm of fork which invites me to keep my weight forward. This lightens the back end which tends to just carry through after the front wheel.
I also think my Vaults have made a big difference as I feel like I'm in, rather than on the bike and feel more relaxed through chatter as they lock your feet securely.
Although perhaps technique is an issue....
Don't hang off the bike of the bike if it's a descent, it's not necessary. Stay balanced with a good lean into the front tyre to keep traction. That butt way back posture is from the days of short travel and long stems. This alone may fix your issue if it's something you do!
As we're at it, have you got your brakes set up for 1 finger? There's a lot less to do for the same amount of control and a better grip of the bars. Oh, and drop your heals a bit too.
Excuse me if this is familiar to you, if not it helps a lot