As you emerge from Domestic arrivals, it's probably easier to walk the length of the arrival floor, past international arrivals and towards the National Express machines, then take the lift from there up to the departure floor. You can not avoid walking the entire length of the T5 building since Domestic Arrivals is the end of north, and the FIrst Wing is the end of South. You could instead do the same walk on the departure floor, where you take the first lifts you come to at arrivals. Departures is busier but you can see where you are heading, from Zone A to Zone J.