Im not sure the measurements but two after market seats might fit nicely if you remove the bench seat. The back of yours seem to low to me.
Overtons.com here in the states has a large selection.
My seats are very comfy and about $200 a pair. Though I changed the seat foam out for firmer and 3/4" thicker to help when in rough water. The cover is snapped on so removing was easy.
The seats I have and others can be ordered in a large variety of colors to suit your boat.
I cant upload pics. Invalid file it says. .jpg should work??
Here is the link for my seat. I have pic in my other posts if you want to see a pair side by side.