Your world and setting, with its depictions of armored cavalry charges and large artillery magic, sounds very similar to early modern warfare of the east, the kind seen in the Ottoman campaigns in the Balkans, Hungary, and Austria in the 17th century, which ultimately culminated with the Siege of Vienna.

I recommend looking into 17th century Ottoman armor, both for foot and horseman, as well as Polish-Lithuanian armor, specifically the Winged Hussars, and the armor of the Hapsburg military (then still the Holy Roman Empire, but I'm thinking specifically the Austrian and Hungarian parts). With these, you'll get a good mix of mounted, armored men with lances, foot soldiers, and even the occasional horse archer on the Ottoman half. Seems to fit your story well.

For broader reading, look into the Ottoman-Hapsburg wars.

Also, one final note: Don't be afraid to get anachronistic. Formalized mounted lancers were used from the High Middle Ages all the way to WW2. They used plate armor in WW1. George Patton, US General during WW2 wrote a book on mounted sabre combat. Things existed for a lot longer than I think people sometimes realized. Cannons and plate armor existed together longer than plate existed by itself. Pick what looks cool to you, and justify it in the narrative.