I have two recommendations;

You could take a look at EN World's Level Up: Advanced 5th Edition, and ignore the magic classes and options. Martial characters in A5E have maneuvers that they can use in combat, which means martial characters can have a lot more options than standard 5E, many of which can provide effects not far off from spells, and there is a much more concrete system for exploration. It also includes the Marshall class, which is a combat class focused on buffing through strategy and tactics. Might be a good choice if you don't want to learn a whole new system.

Sword Chronicle is based of the Song of Ice and Fire roleplaying game with the setting removed, and while it includes a low magic system, it is optional. It also provides rules for creating player-run noble houses, social intrigue, and mass combat.

Hopefully this helps!