Small safes ~ more than sufficient for your purposes (I assume you are not Prince Phillip and your wife is not called Elizabeth) can be purchased from Screwfix or other suppliers for less than £50. They can be bolted to the wall or floor inside a cupboard and jewellery, papers and cash can be safely left in them.
My inlaws used to go through this "We've hidden your mother's jewells (mostly tat) in the loft, under the insulation, the insurance policies are under the lounge carpet" nonsense everytime they went anywhere. FFS they have been known to hide stuff when they went to the shops and thence onto lunch. These same people refused to switch on their answer phone in case burglars rang their ex-directory number and, hearing the answer machine, deduce that they must be out and therefore would come and break in
I bought them a small safe (from Makro ~ cost £45, guaranteed fireproof) and my BiL, equally exasperated, installed it for them in their bedroom. You have never seen two such happy people in all your life.
They then used to ring either me or BiL to ask us for the numbers to open the fvcking thing because they could never remember them ~ despite the fact that they were the FiL's date of birth
