As far as I am aware there aren't many companies that are offering that 'unemployment' income protection.
I am only familar with the product that Assurant Solutions have on the market.
The cover pays out a monthly benefit if you are unable to work due to accident, illness or involuntary unemployment.
In relation to their specific mortgage payment protection, it offers cover up to 125% of the mortgage repayment. This extra 25% is to cover associated mortgage and property related expenses such as home insurance, utility bills or life insurance premiums.
I'm sure if your boyfriend is joint holder of the mortgage, it will only allow cover for half.
Now, I'm personally not familar with their products, so the above is only what I'm aware of.
Thanks
J