Louvre or Musee d’Orsay? Make sure you know what you prefer, as they’re pricey, have huge queues and are absolutely vast (if you’ve never been to the Louvre before, it’s far bigger than anything else comparable and you won’t manage to see everything in a full day even if you wanted to). I second the Orangerie museum. Also Pere Lachaise; if dead people are your thing then the Catacombs are fun.
Boat trips there is a river bus a bit like the one in London which is cheaper than the tourist ones albeit no commentary etc.
Spend half a day wandering round the Left Bank (5th/6th arrondissements) university quarter, Latin quarter, Rue Mouffetard, Jardin du Luxembourg and so on.
Definitely go up to Montmartre and Pigalle if you can although that’s not great for someone who struggles to walk far.
Food is very hit and miss. I’ve had some terrible meals there, but last time I was there we ate pretty well. I prefer to take an apartment, that means you can pop to the boulangerie in the morning for a “baguette tradition” and some croissants, and have the leftover baguette in the evening with whatever I’ve picked up from the fromagerie, maybe a heated up tin of cassoulet and a bottle of rouge. Then some macarons for dessert or whatever else took my fancy from the patisserie. There are places where you can take an apartment for less than a week.
Touristy but do have a posh cake/hot chocolate at Angelina’s (Rue de Rivoli near the Tuileries). Try not to look at the bill when it arrives, but it’s a great 5 star experience.
If you don’t want to do the metro then buses are pretty decent, obviously a bit slower.
It’s really expensive. But if you’re near a decent metro line (or RER) then you don’t have to stay centrally as you can get in very quickly.
