Basel Switzerland to Carcossone France.

Fastest is 7 to 8 hours with 2 train changes. Connection times from 8 to 19 minutes. SBB is showing me 236 CHF, or about $270 US for 2, 2nd class. Check for yourself at www.sbb.ch/en

Since Basel is an EasyJet hub, you might look at a flight to Toulouse and the rest of the way by train. Might save some money and a little time.

Swiss trains typically run on time and most French ones do too. Consider practicing at home with how you would carry all your luggage during a transfer from one train to the next. There really aren’t any porters to carry luggage for you.
SBB will even tell you which tracks the trains run on so you can understand how far you need to get from one train to the next.
And of course, be one of the first to get off the train to make sure you get out quickly to get on the next train!
Have fun and good luck!

your physical age is much less important than any mobility or vision impairments you may have...

You need to move you and your luggage under your own steam, unless disabled and using booked accessibility assistance, and you will need to consider if you can manage stairs with your luggage or if escalators (if any) will do, or if you need lifts (elevators), all of which may add some time.

I travel with a disabled person so speak from some experience.

Where do you need to change trains?