Heathrow to Waterloo Station

No direct trains/Underground, or even bus to Waterloo Station.

Your Options are:

For direct, a Taxi, but $$$

Cheapest, The Piccadilly line from Heathrow to Leicester Square station, switch to the Northern Line to Waterloo. Maybe ~1 hour.

For a bit more cost, but faster, would be the Elizabeth Line to the Northern Line; Maybe ~45 Minutes.

You can use the planner https://tfl.gov.uk/plan-a-journey/ to lay it out, plus see info on accessibility.

I was recently in London and stayed at the Premier Inn County Hall, which is near Waterloo station. To get there I caught the Elizabeth Line train (Abbey Wood) at Heathrow and took it to Tottenham Court Road Station. From there, I transferred to the Northern (black) Line, which took me to Waterloo Station. It was very easy and not too expensive. Definitely cheaper than a taxi.

And while there are stairs at the stations, you can also take the lift. I had luggage myself so that’s what I did..

Are you staying near Waterloo?

You could also pre-book a car service. It will meet you as you exit customs and drop you in front of your accomodations. They will help with luggage. You will know the price when booking.

Cheaper than a taxi but more expensive than public transportation.

From Heathrow, I would take the Elizabeth Line to Bond Street, then the Jubilee Line (3 stops) to Waterloo.

The step free route is to take London Bus #490 (a single deck route) from outside Terminal 5 to Feltham Station (in Zone 6), then a frequent South West Trains service to Waterloo. That route is as fast (often faster) than the tube or any Elizabeth Line route.

Bus and rail come under TfL ticketing rules (the daily cap etc). In the peak trains from Feltham can be busy, but not mid to late morning. The 490 runs every 12 minutes.

Because the route serves the airport they expect luggage, and locals from South West London (if not tourists) use the route for that purpose.

I'm wondering if you are going to Waterloo for a hotel - then the various choices above would work - or do you want to get a train from there? If it is a train, there may be other ways of getting to your destination...