Would I be better off with a solo canoe or a tandem, shared cockpit kayak?

Pertinent information:

I fluctuate between 130-140 lbs, 5’ 4”.

child is approximately 5 years old and ~40 lbs now.

They have a rare disease that affects joints and their back so I will most likely always be paddling solo and hauling their weight +. They walk, talk, dance, sing, swim, etc. on their own.

Need large dry bin or space for larger dry bag. Has to fit cooler with two 16oz, wide mouth mason jars & ice pack along with other normal day trip stuff.

Day trips only.