Hello Frau Dr. Michaela Beinert, 
 
Thanks for your question. 
 
Unfortunately, we cannot do custom sized mattresses in our Origins range. 
 
We can however, do them in our Artisan range. 
 
It might be worth looking at something like the Artisan 1500 with a Firm spring tension dependent on the body weights of the users;
 

 
The Artisan 1500 has a medium feel in the top layers; It is the firmer end of medium but still gives that slight sink into the top layer but not too much. This aligns with the Origins Pocket 1500 / 2000 - That model is similarly a medium feel in the top layers but the Firm (2000) spring count accommodates body weights of 17 to 23st. The Firm spring tension on the Artisan 1500 will do exactly the same.
 

 
You would have to pay an additional 10% on the standard cost of a King Size Artisan 1500 to increase the width to 160cm but please note that non-standard sizes aren't covered with our 60 day love it or return it guarantee as we have limited resale ability on them. Please see our article here for further information on bespoke sizes.
 
I hope this has answered your questions fully but if you do have any further queries please don't hesitate to contact our office on 0161 437 4419. We are open Monday to Friday 8am to 8pm and Saturday and Sunday 10am to 4pm. 
 
Kind Regards, Lee.