I think the key will be to pre-book assistance (both at LHR and WAW) and to ensure an early arrival. Other than that I see no reason why things should not proceed smoothly. I think a lot of us think others will find airports are stressful because we find them stressful. That in turn is because many of us are often flying for business, pushed for time and try and run a tight schedule with little slack for things to go wrong- that causes stress. For the occasional leisure traveller with plenty of time on their hands the airport experience might even be fun