Lift to get someone up off the floor?

Never try to get someone up off the floor yourself. This can cause serious injury to them and you.

If someone is on the floor, call 911. Let the paramedics handle it the correct and safe way.

You call 911 and ask for a "LIFT ASSIST"
In most areas the call and response will cost you nothing.
If they transport to the hospital that is where the $$$ comes in.
Paramedics will ask someone to sign a waiver indicating that you have declined transport.
BUT what calling 911 will do in addition to getting dad up off the floor is the paramedics will know there is a vulnerable person living at that address. They will know dad and whoever is caring for him. Dad will know them and not be overly frightened when they show up again.
AND..They are trained to help someone up. They are trained to that they will not hurt dad or themselves.
What I used to do was while I was on the phone talking to the dispatcher I would lock up the dogs, put a note on the front door "door open walk in" and then I would go back and sit with my Husband. The paramedics would walk in I would call out and they would go to the room where we were. Did this 9 times was never charged, the guys were awesome usually in and out of the house in 5 minutes.
I probably would never have been able to use a "device" as my Husband would not have been able to comprehend instructions.

The "lift" you're after is called 911. Either the EMT's or firefighters(depends where you live)will come out and pick up your dad for free as long as he isn't hurt and need to be transported to the hospital.
No lift on Amazon is worth hurting oneself over or your dad.
Perhaps a visit to his doctor is in order to find out exactly why he is falling in the first place.

My late husband who'd had a massive stroke at 48, ended up developing vascular dementia in his late 60's and became a fall risk. There was a 2 month period when I had to call 911 9 times to have them come get him up off the floor and into bed.
And each time they came they were very kind and professional, and there was no charge.
Please don't risk hurting yourself or anyone else.

If dad is in such bad condition that he can't get up off the floor, he may be unable to get into this device. Or be unable in the near future. A lot depends on his condition and prognosis. Like, why's he falling in the first place? Are his limbs floppy sometimes? Does he have issues such as a sore hip that would keep him from rolling on it?

Also, you could hurt yourself trying to help him.

The best advice is to call EMTs and have them get him up when he falls. They are professionals.