Auto parts stores sell a special hose for brake boosters. It is described as 11/32" vacuum brake hose. It has a thicker hose wall and won't collapse internally, and being a slightly smaller diameter you don't typically need hose clamps if using it on a hose nipple fitting (though you can clamp it if you like).
For a hose run as long as yours (booster under the floor) I would recommend 3/8" hard line from the intake down along the transmission to near the booster, then a piece of vacuum brake hose from the hard line to the check valve on the booster.
At very least replace all the hose you have with the special hose.
Once all that is good, we can look at brake pressure at the wheels.