May I suggest Titan covers. I have a fitted one for the drivers seat and a 'loose fit' one for the rear seat which the dogs use. They are based at Hinckley just off the A5. They do postage. The fitted cover completely encloses the seat including the head restraint.
Honest, these are as tough as old boots. I hope I'm not breaking any rules by providing a link. They also do damned good dog beds which have proved to be indestructible. The beds may not be cheap, but they last and work out to be cost effective. The company also uses the name of 'Over the Top'..... They have a tab on their page leading to seat covers. It is the same unit/company. I am not affiliated to the company in any way, I have just bought from them and think it is damned good quality stuff.
https://www.titancovers.co.uk
https://www.overthetop.co.uk/dog-beds-mats-and-throws/