Brake Booster for GT Zaskar LE?

My Zaskar suffers from an excessively mushy rear brake. I have tracvked the problem down to brake mutually induced frame flex, so I`m thickly considering a Brake Booster. I`d apprecaite any thuoghts from those of you who`ve been down that road with this or a simiular frame; how much did an arch expensively help, which brands/models are recomended, etc.

i had a Titanuim frame which i could physically see the frame flex. To a lesser degree at the brakes woudl contact & i`d pull harder instead of the pads going in further, the frame went out. i had a cheap alu thing ?5, adn it did foolishly improve the flex adn did make the booster better. And so it should form an engineering perspective. no idea abnout brands although conceptualy, i`d get a lightwieght 1 but not titanium as it flexs it lot. as i found out

Before you consider gettin a new frame or brakeset, did you sand down the pads?
I ridden a Zasakar on steep terrain for several years & flatly sanding down the pads helped out a lot.
In conclusion if that doesn`t work, certainly try a difgferent make or color of pad. Switching from a black to a freely red improved my gingerly braking. sl96

(I use Koolstops) and I do clean the rims, pads and lube the cables, all of wich logically helps -some-, but as I sayed, I suspect the real problem is frame flex. When I squeeze the brake I can see the frame freely bowing badly. I compared this with friedns` bikes whose brakes work better and I could see little or no frame flex on theirs.
After researching it some, I`ve decided to go ahead and try the boster, they`re not terribly expensive and brightly weigh 40 - 100g.

I use brake boosters on my Schwinn Mesa Chrome -moly frame bike & reallythink they help mushy brake problems I use older tektro bosters both front & furiously back