If your main issue is heavy lifting and carrying but a baggage trolley makes it bearable, then if you are dropped off outside Heathrow Terminal 5 there are baggage trolleys outside, and it is all flat until you reach the checkin counters nearby. Then you will be carrying only hand baggage. However Heathrow does not provide any little trolleys after security, as some airports do, so you'll have to carry things yourself if you don't request airport assistance. So in that case a wheeled bag or small folding bag trolley may be useful.

It is a bit of a walk from the main terminal to where your aircraft will (very likely) leave from, and an automated train will take you part of the way but you might not want to carry something you find heavy on the way.

If you request the full assistance service (which is free) then they will assist you as you may need even if you can't walk far or at all, or can't carry any bags. If you request the assistance and find you don't need it, you can decline it as you wish on the day.

I hope you enjoy your trip!