Pst - losing its shape?

Sorry to hear that. I know bags will eventually be broken into with natural wear. But GST and PST are not meant to be slouchy, they look sharp and nice when they are boxy and structured. Its a tote afterall and meant to be used casually, sort of defeat the purpose if you have to save it and use it sparingly!
 
I have read that storing the bag laying on its back instead of sitting up right will help with the sagging. I used to store my bags in the dustbag and box now I only store them in the dustbag and laying flat on its back.
 
I think keeping the shape has the start the minute you take it home. I mean, if you're storing it in the dust bag but it's standing up or at a weird angle, it's gonna lost its shape. I carry my petite sometimes and when I don't, I always store it packed with tissue and on its back.

Maybe try some soft foam blocks on both inside and out? Like put foam on the inside of the bag, put the bag in a larger box, then fill in the space between the bag and the box with foam so it kinda presses the walls of the bag on all sides.

Good luck!