Cathinjoetown

I vote for Green Prk as well, smallish station.

Grindeldoo

I agree with Cathinjoetown. You'll probably find people more helpful at Green Park as well - plenty will be going your way. In the City (Bank) it tends to be more hectic and every man/woman for him/herself. Jubilee line trains go every 2 minutes in the rush hour, so you won't have to wait long. I recommend that you check at Heathrow that trains are running normally on the Piccadilly and Jubilee lines. They usually do, but it's as well to have your Plan B ready in case there are problems.

Yelpir

Thanks Cathinjoetown and Grindeldoo