The primary concern is mounting the seat (or seats).

The factory seat has fixed anchor points that are reinforced. Putting in a high-back bucket seat means you will need to provide for new reinforced mounting points for the seat bracket.

Then, you need to ensure that the seat belt points match the seat. The upper shoulder mount is high enough and the belt should be be long enough to use.

Stepping into some arcane legal points, your desire to provide better head restraint is noted. Now, in the case of a rear-end collusion, should the seat come loose or should an injury still occur, you could face lack of coverage for modifying the factory design which has undergone specific tests. Your mods could nullify your insurance.

Again, your idea is possible. As you are modifying factory designed, do it right and provide for new reinforced mounting points.

Seat belt extenders (and new seat belts) are available. Check http://www.omix-ada.com/ for detailed parts availability.

You may be able to start with the factory front seat brackets as your new base.