Hello. Google “Seine River cruises online” and there are a lot of suggested sites. Enjoy your trip!

I am not sure that there are hop an hop off boats on the Seine

There is a Seine fiber cruise as a hop on and hop off. Cost Round 20 euros. I use Viator to book trips in advance

Hi Anna - My husband & I just took pot luck with this - it was raining in Paris on the day - we just wanted to get to the Eiffel Tower and from there walk back to our hotel - we came out of the Louvre and went to the river - saw a kiosk which was a ticket sales - bought a ticket each & travelled back and forth whilst it rained and got out at the Eiffel Tower point after being on the boat for several rounds of the route it took - after about 3 round trips we got out finally after seeing it from the river- rained for quite a while this was in 2010 - things change but I am sure you would still be able to do this. Worth a try. Have fun & enjoy Paris whatever the weather is. We did and it has been very memorable for us.

I like the one on the right bank not far from the Eiffel tower. That is what we use for work. Time it so you leave in the daylight and come back for first eiffel tower sparkle if you are looking for magic or romance. The only thing I know for sure is not to go on one with dinner. Apparently they are systematically not worth it with sad food. In general if you are in a tourist area with tons of restaurants and the menus are in 3 languages with a guy standing in the door to pull in tourists, walk to the next parallel street or two to find a real restaurant. This applies world wide. Enjoy!

We went in october and it was fine, we found the atmosphere on the boat ok

Yes they have a designated smoking area.