Re mjs’s comment about the Citadines not being near a park - it is fairly close to St James’s park. Less than a 10 minute walk.

I so appreciate all of your comments (especially those that help me to really comprehend what are the aspects of and differences between various neighborhoods that on a map all look as though they should be similar.) What I really need to do also is sit down with each place I am considering and really figure out how I would get to the airport from there--which line and if there are transfers that would be a big hassle.

A couple of you have said about yourselves that you're picky; I too am picky about lodging. I typically find that doing the extra legwork in advance of booking tends to pay off and I enjoy my lodging. But, I have decided I am not going to be obsessive about this as I have sometimes been with past trips. Between all of your suggestions and the comments you have made, I am going to narrow down my choices from places I have already seen and be done with it rather than obsessively seeking out that illusive absolutely perfect place.

Thanks again.

Good luck, it's always difficult if you haven't been to a place before. Don't let perfect be the enemy of good. There is always the option of taking public transport to whichever station gets you closest to your chosen hotel and then taking a short taxi ride there.
London is so fabulous,I hope wherever you choose to stay you will have a wonderful time. If you have anymore questions at all we are here.

You can always leave luggage in the lockers at the train station. I have done that in Venice and Naples.

That's a possibility -- but most of the mainline stations Victoria/Paddington/Waterloo/Kings Cross etc etc are sort of in a circle around the center. So you'd want to book a place that is both easy access in from LHR and near the specific train station. They don't have self-serve 'lockers' as such but a left luggage office and you might have to queue to drop and collect the bags.