I have a set of Volvo Rsport seat covers available from my car. You can see them below fitted to my 740.
These covered fit over the existing seats (to fit them, the seats do need to be removed to fit them but it only took my half a day to do mine and I am willing to help if you want them fitting here) and have very pronounced side-padding on the front seats, helping to hold you in.
The set also comes with door inserts which you can see in the pictures below.
I know of only two sets (including these) in the UK so they do not come up for sale very often (I had to import these from the states.
Price - £400 plus shipping.