If you want it slightly higher than the single height but not as tall as the double height you can get the single height version with legs - but that costs about £60
KALLAX Shelving unit with underframe, white/white, 147x59 cm - IKEA
Ah ok - how much weight does the kallax take? I know people used to put Detolfs on top of those.
Extra shelves for the barney wouldn't solve the height/fall risk issue for a dwarf hamster - it would need to be a full level - which is a bit of diy.
Your best option would be the Elmo cage which is basically a much lower height Barney cage! No diy - it's 35cm high and perfect for a dwarf hamster. But it's only available in Germany - and they won't ship to the Uk now - maybe they would ship to Norway?
They don't call it the Elmo any more
PETGARD XXL Mouse and Hamster Cage : Amazon.de: Pet Supplies
See if they ship to Norway? They might do as you're in the EU. If Amazon don't you could check on Petgard's website.
Mause- & Hamsterkafig ELMO "XXL"