I am staying near Disneyland Paris but wish to go into Paris for the day. I am planning to go up the Eiffel Tower and on a boat trip. I am a wheelchair user. What is the best / easiest route to do this? Thank you!
Wheelchair accessible Paris RER train stations are listed here, Disneyland / Marne La Vallée station along the RER A train being one of them. When boarding RER trains, wait at the head of the platform where the conductor's car will stop so he can see you. The conductor (or station staff) will setup a portable ramp you can use to wheel onto (and later off) the first passenger car.
The entire Paris Bus system is wheelchair accessible so buses around Paris city centre are your best bet. So, getting to the Seine river boat you'd like to take will be easiest by bus. Only Metro line 14 is wheelchair accessible with elevators and train cars that have easy roll-on access.
There are several boat companies along the Seine and they have different departure points. If you find which one you'd like to take, you can search for a bus route or ask and I can help you search.