Lovely thread, lots of ideas here I am going to nick myself. A couple that have not come up yet that worked well for us at that age:
Cards and dice. A normal pack of cards is brilliant: flip two and he adds them (or multiplies them once he is ready), highest total wins the pair, a bit like a maths version of snap. Dice are the same idea, roll two or three and race to add them. It is quick, it is competitive, and it does not feel like practice.
A "number of the day" game. Pick a target (we used the date, so the 14th means 14) and see how many ways he can make it: 7 plus 7, 20 take 6, double 7. Brilliant in the car or waiting anywhere, and it stretches him without feeling like a quiz.
Cooking, properly hands on. Halving and doubling a recipe is sneaky fraction and times-tables practice, and weighing things out is measurement without him noticing.
The other honest thing I would add: some days I just do not have the energy to invent sums, and that is where a short app session saves me. Something that adapts to where he actually is can keep the daily habit going on the days real life gets in the way, even if it is only ten minutes. For a keen reader who is a bit lighter on maths, that little-and-often approach is exactly what closes the gap, so you are already on the right track just by thinking about it.