thanks for the details - but I think I can't help on the most important points (like the Paris accommodation).

Concerning the hop-on hop-off: I've done this in several towns, but never in London or Paris. I'm not sure if it exists in Paris at all. London has several of those tours, but I found it more convenient (and probably cheaper) to have

a travel pass for subway and busses and then use the normal public transport.

Two ideas for London (but I don't have web adresses at hand): What about doing a London walk? It's a well-known company who does walking tours to certain topics (do a search on the internet). And a thing I wanted to do several times but never managed to - there is a possibility to attend the closing ceremony of the Tower, but only if you arrange it in advance. Years ago I tried to attend it, but had no chance during my visit (summer is very popular). AND it was really complicated to book it in advance, but maybe they made the process simpler now.......

And an idea for Paris: There is La villette which also has a longer name I can't recall at the moment - it's a big technique museum. With a wonderful garden including e.g. a fog garden. And it has (or had at least some years ago) a kind of flight simulator which you could try out AND afterwards see it from the outside how it works..... Unfortunately we didn't manage to get inside the main building cause we had the wrong (too long) opening times.

hth Baerbel (Germany)