I don't play historicals. So I can't recommend any specific kit. That said, there are a bunch of options because "knight" isn't a copyrightable thing.
Off the top of my head. Oathmark, Deus Vult (aka FireForge), Victrix, Barons War, and maybe Frostgrave.
There is a YouTuber Paul Stanley (not the singer) that has a bunch of videos on the topic if you want details. This is the first one of his to come up when I search.
https://youtube.com/watch?v=tFHfvvUbljYThe basic gist is this. You go for GW for your set piece units. And then for mass infantry you go third party, perhaps with some official bits to sell the illusion.
Frostgrave is the odd man out since most of their kits are winter or jungle themed.
Oathmark is supposedly a modern take on an old world style fantasy rank and flank game before GW brought it back, and is where I'd start my search. They have fairly generic factions like orcs, undead, and elves.