A chair that is wrong for a man does not look wrong. It looks like the chair he has always used, and he will keep using it until a bad stand-up makes the problem visible. Fitting it to him is a measuring job you can finish in one sitting, and it tells you whether to change the chair, the cushion, or the table before anyone spends money.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Measure him in the chair he uses
Have him sit in the kitchen chair he uses every day, feet flat, in his usual posture. Measure from the floor to the top of the seat, then from the floor to the back of his knee where the seat edge sits. Measure seat depth from the back of the seat to the front edge, and check whether his back meets the backrest without him leaning forward. If the chair has arms, note their height against his elbow when he rests his forearm.
Check the table and the push
Measure the gap between the table edge and his stomach when he sits upright. He needs room to pull in and push out without bumping the table, and a gap that is too tight means he will lean forward to stand. Then have him stand from the chair while you watch. Note whether he uses the arms, pushes off the table, or rocks forward. Each of those is a fact you can write down.
Check the chair itself
Look at the legs on the floor he actually walks on. A chair that slides on tile when he pushes back needs glides or a non-slip pad. A rocking chair or one with a loose joint should be tested before he sits in it again. Check whether the seat is level, because a tilted seat is a sizing problem too.
Compare the three fixes
A seat cushion raises the seat without changing the chair, so it helps only if the seat is too low and the backrest already fits. A different chair with the right seat height and arm height fixes more but needs room and a delivery route. Lowering or moving the table fixes clearance without touching the chair, but only if the table can move. Write the measured numbers beside each option and see which one closes the gap you found.
Your next move
Tonight, measure the four numbers above with a tape measure and write them on a card. Ask him to sit in the chair while you note how he sits, framed as a look at the chair rather than a test of him. Then bring the card to whoever is choosing the fix, so the decision starts from his measurements and not from a catalog.