Without being you ,looking out your blind window,over your field of fire? I could recommend things that would not fit you,and would not be worth a hardly.
I suggest you go to your blind with your rifle.Figure out what is best for you to sit on.Is there any form of bench or table?
A hanger strap from above,ala huey door gunner?
Put a bunny ear bag on top of a camera tripod.
A small table to rest your elbows on. A sandbag or two to support your forarms. Good for your coffee and Pepperidge farm goldfish,too. A bag of powdered sugar donuts,a few krautburgers and a dozen tamales..Now you are set!
Look.Ponder.Drink coffee.Spend pre season time there.A simple,elegant plan will form in your mind. Make something.No need to spend money at cabelas.
A plastic laundry detergent jug with the pour insert removed from the neck makes a great used coffee deposit jug.You said you are an Old Guy.
Drape a heavy wool blanket over your chair before you sit down.You'll figure it out.Don't forget your slippers.