If you decide to make your own mix I have a tool you can use. I always tell people, it is just a tool, not a substitute for your own research.
Here it is:
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The "target values" are configured for gerbils of course but there's zero research on dwarf hamster nutritional needs anyway. Please do read through the accompanying notes. They are long but they take you through each nutrient and explain how much various different rodents need. Your partner's knowledge will of course help a lot too.
I don't think Harry Hamster is that bad for a Russian/hybrid dwarf in your situation, especially if you mix in some extra small seeds and grains.