Do you know the measurement ??
Funnliy enough Ive had the same problem, my down staircase is 71.5 and I thought there was nothing. Ive been searching for weeks for a pressure fit and have found this one in JOHN LEWIS , which was the narrowest. I looked everywere mothercare/jo jo maman/toys r us and others.
If its narrrower than this then Im at a loss. the only really narrrow one is the kiddygaurd roller blind style , by Lascal ,but thats a bolt on one.