(Surcoat over mail, Steppe horse, Nomad bow, Tatar arrow, Espada Eslavona, Light Strange helmet, Black leather gloves and eastern lamellar greaves).
Quick suggestion:
Most horse archers don't bother with a melee weapon at all, opting to use the slot for more arrows.
If you prefer to have a melee option, though, I'd recommend replacing the Espada Eslavona with a different sword. It's quite expensive for a backup weapon (535 gold per repair), and isn't really suited for use on horseback (You don't really benefit from it's high thrust attack, and you definitely suffer for its short, weak, slash attacks).
Cheap backup weapon for cavalry use:
The Arabian Straight Sword has greater reach (+10) and greater damage (+2 on slash) and only costs 148 gold on repair. It's so cheap because it has an absolutely worthless stab attack. BUT, you're on horseback so you don't really care about that.
There are plenty of other weapons in that cost range that would make perfectly serviceable weapons for self defense when dismounted. Pick one that looks cool and go for it! (I used a 4 upkeep club on my archer)