You could totally remove the section with the drawer. Take out the table and you might have space for a recliner.
I would leave the section over the heater intact.
You could also build a L-shape curved bench in the space left by removing the dinette bench, and curve it on around the wall. A bench can be really comfortable if it's covered with properly made cushions.
If you google "upholstery foam" you will find all kinds of online suppliers for foam. The foam comes in different shapes and types of foam.
You could also get a local upholstery shop to make up some good cushions for you.
If you do some looking, you might find a sectional sofa where you can get a short section with a chaise for the corner section.
Or take out both dinette sections, which might take some carpentry work to cover the heater. Put a futon in the space.
Lots of options, depends on your budget, tastes, and space.