If your cold water overrides your hot water, simply fit a resistor tap valve in your cold water tap and this will balance out your pressure problem. Restrictor tap valves are available from any plumbing or hardware store.
When installing a handshower remember the round nut on the hose fits onto the wall end, either on the supply elbow or bracket. The tapered hose nut screws onto your handset, so that it slots into the cradle of your bracket or rail holder.
When choosing a handshower first make sure of the water pressure at the residence. If it is mains pressure you can choose any Gracott handshower. If you have low water pressure, purchase a Gracott handshower suitable for low water pressures.