Have you looked at the white rose materials as they have lots of ideas. I also use the ncetm reasoning documents for ideas.
In addition I use the following:
what if ... Find all possibilities. E.g. 2 numbers add to make 10, what could each number be ? Find all possibilities. What is I had 3 numbers?
Other ideas are Always , sometimes , never eg if you multiply a number by 10 the answer ends in 0?
If I know .... then I know.... eg if I know 9+1=10 then I know 90+10.
Odd one out or what's the same what's different ? Give 3 things (number or shape) And ask either what's the same what's different or ask which is the odd one out? Get Children to explain their reason
If the answer is 20, what could the question be? Find an obvious question, a general question and a perculiar question (POG)
Hope these ideas help