That circuit is OK, although personally I would reduce the value of the pullup resistor to +6V to 2k2 or 4K7, at the expense of slightly increased current consumption when the H-bridge is powered up. This resistor will only draw current when the transistor is turned on and the H-bridge is powered up, so it doesn't defeat the purpose of switching the H-bridge supply.
As you have a little under 6V gate drive available, you will need to use a logic level P-channel mosfet.