A test gain yes just to see what you think is a good plan.

I am usually the largest woman in any given place I go.
I love trying new eateries and trying different things.
Went to a little Mom and Pop place I had never been to and had a wonderful Ruben sandwich and some amazing vegetable and rice soup.
They had home made pastrami so I took a pound of that home with me.

Even with a belt they slip down?
Some larger guys wear suspenders so I guess that is an option too.
I guess it all depends on what shape your belly is.
You may have to go to a tailor and get fitted properly.
I hope you get the problem worked out.

I checked out your pics and you are built like a guy I dated a few years back and he wore jeans that had some stretch to them and they stayed up for him.
Most guys jeans have no stretch at all so no give I can see them sliding down.

Try a larger size seems the sensible approach.

I do stay off peoples lawn chairs tho'.
I stick to picnic table benches if they have them.
I did squeeze my big ass into a wooden rocker at Cracker Barrel and it held just fine.

I have gotten used to chairs and couches creaking when I sit on them.

A persons health comes before your personal fetish.

I broke a wooden lawn chair once.
I was 425 at the time.

Sounds a little one sided to me.
I think you need to make your concerns known to him.
Sweetoothsweeheart makes a lot of sense.