Hey Jmac and welcome. The bagster cover is just that, only a cover. The foam itself doesn't get changed. Like you I'm over 6' and find that I'm sat on the back of the seat and find the foam compresses and I'm sat on the base. I've had some quotes for a seat rebuild, but still umming etc...
I see you're in Farnham, I've got a good mate there with a BMW rs. I'll tell him to look out for another Ten.