The vacuum you pick now has to fit the floors he actually walks, not the ones in the catalog. Mom probably knew which rugs needed the long hose and which needed nothing at all. Dad has the house now, and the machine should suit the house as it is.
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.
Start with the floor, not the box
Walk the route he takes on an ordinary day: bedroom to kitchen, kitchen to his chair, hall to the bathroom. Note the rugs he crosses, the bare boards, the threshold strips, and any stairs. A light stick model that cannot grip a thick rug will sit unused in the closet, and a heavy upright will make the hall feel like a chore.
Match the weight to the person who lifts it
Lift each model in the store or the one already in the house. Can he carry it up one step with one hand? Canister and upright bodies differ a lot. A lighter cordless unit often gets used more than a heavier corded one, but a battery that runs flat halfway down the hall is its own problem. Check how the battery comes out and whether swapping it needs tools.
Measure the cord and count the outlets
Measure the distance from the nearest outlet to the farthest corner of the bedroom and the hall. If the cord will not reach the middle of the living room without a second plug, a cordless model or a longer cord fits better than a bigger motor.
Check the attachments he will reach for
Look for a floor head that switches between hard floor and carpet without tools, a crevice tool that reaches the gap beside the bed, and a dust bin that empties without a lot of bending. Attachments that need a screwdriver to change tend to stay in the box.
What to do tonight
Take a tape measure to the hall and bedroom. Write down the cord reach, the widest rug, and which rooms have bare floor. Ask him, lightly, which room he would vacuum first if he were doing it himself. The answer will tell you more than any review.
When to ask the doctor
If pushing the vacuum leaves him short of breath, sore in the back, or unsteady on his feet, mention it at his next appointment and describe exactly what he was doing. Stop and sit down if it hurts. Choosing a lighter machine or having the floors done another way is an ordinary fix, not a sign that something is wrong with him.