Steam Link: http://steamcommunity.com/sharedfiles/filedetails/?id=679539739
This is a simple mod which does exactly what you think it does. It adds standard bearers to cavalry units! In vanilla standard bearers only appear in infantry units and none exist for cavalry. I don't see any reason for this as cavalry units did indeed have standard bearers in real life.
History aside I find that this mod adds a bit of flair to the cavalry units and makes them look much better, especially since their standards are held higher and stand out very well with cavalry's smaller unit sizes. In a cavalry v cavalry fight you can see the two opposing standards bobbing and weaving over the fighters, which is a nice detail to see when you zoom in to see Total War's great animations!
This mod should be compatible with everything, including unit mods and reskins.
If you would like to check out another great mod then see my latest mod Sebidee's Charlemagne Expanded - Unit Roster Overhaul. It's a complete overhaul of every playable roster in the Age of Charlemagn campaign and it will very shortly recieve some huge updates, so you can look forward to that!
Thanks and I hope you like the mod!