JR Farm Feast for hamsters on Zooplus is about the best hamster mix I can think of for variety of ingredients. I never found the lower protein it has an issue when I tried it in the past, but my Syrians didn't particularly like the small seeds it contained! Their dwarf food has more protein but also more small seeds that I find Syrians turn their noses up at. For that reason I wouldn't particularly recommend them to a Syrian owner, unless you know your Syrian isn't picky over small seeds!
Slightly potentially controversially, I actually am using the JR Farm Feast for rats as part of my hamster mix at the moment. It has a very similar nutritional analysis, and identical nutritional additives, as the hamster version, but has fewer small seeds so my Syrians eat pretty much all of it. I mix it with Versele Laga Hamster Crispy (also on Zooplus) and some wild bird seed (which the Syrians do tend to ignore
so I probably won't add it next time) and my hams are generally in good condition and do well on it.
There are also a couple of hamster mixes with a large variety of ingredients available on ratrations.co.uk, but those need to be fed with some form of vitamin supplement as they contain no additives like the more commercial mixes do. Again, I found Syrians a bit picky over the smaller seeds (and some of the other ingredients like bran flakes) in them when I tried them in the past, so wouldn't particularly recommend them for that reason. I have been tempted to try some of the rat mixes on ratrations as an additive to a mix though! They also sell dried veg and herbs, and just straight seeds and grains, if you want to add those kinds of things to a basic hamster mix.
(The mix on ratrations.co.uk called "Lavender's Hamster Mix" I have not tried myself, it's the other hamster mixes on there that I have tried, just to let you know!)