I have the flavoured coffees too and have a bit of sweetener in them despite not usually having sugar/sweetener in my coffee. They do feel like a real treat.
I have sponge fingers (like you use in trifles) instead of biscuits, they're only 1 syn each. Or I use hifi light or alone light bars as a HEb.
I made a 'trifle' last night and it was flipping lovely! I just stuck a Harley's ready made sugar free jelly (1/2 syn) a banana and custard muller light and some total 0% mixed with a bit of sweetener and vanilla extract into a bowl. It was huge and really satisfied a sweet craving.