Hi guys

I know this has been asked before but could someone please point me in the right direction regarding a Fillet query.
I want to create a 1 or 2mm fillet on the top surface as shown, I have tried scaling the model up without success. Is it because the surfaces are too complex if so were would I need to simplify them?

Also I will need to shell the model and have tried and failed, I guess I will need to copy & scale down then booleon subtract?

Any help will be gratefully recieved.

Alexander