i add wheatgerm, oatmeal or porridge oats, cinnamon or mixed spice (not altogether though!) I avoid nuts for allergy reasons but the flavour would be good. Mixed spice is good for berries and apple. Always demerara sugar sprinkled on top.
I have a recipe for a crumble topping for apple which includes cheese - I was sceptical about it but tried it and it was nice, you can't taste the cheese. I can look it out if you like and I'd agree with oats.
I do half flour half crushed almonds, a spinkle of cinammon/mixed spice and some demerara sugar. Then poke little holes in it with a skewer. The holes create 'pockets' where the sugar goes all toffee like - yummy!
Here you are lucysmam, 130g plain flour, 75g unsalted butter, 50g porridge oats, 150g golden/Demerera sugar, 150g Cheshire cheese.
Sift flour, rub in butter to breadcrumbs Stir in oats and 110g of the sugar Break the cheese and scatter on top of the apples then put the crumble on top of the cheese. Bake at 190/gas mark 5 for 25 mins or until the top is golden brown. Let me know what it tastes like.