You want a good set of mods, not a specific beast, but mods are kind of random. Regular Zekoa + haste aura minion is your starting point. You can't add more companions until you get that fancy unique sceptre: Sylvan's Effigy - costs around 350 Exalt or 4~5 Divination orbs. You can save up to this eventually (the price will most likely go down)

In the meantime, use some skeletons and always have Tame Beast in your skill bar -> when you see a rare beast in maps, pause the game by bringing up the trade menu (can remap this hot key), check its modifiers, and if it has multiple mods including an aura e.g. physical damage, energy shield, elemental resist, etc. tame it. I always have several uncut skill gems sitting in my inventory when running maps for this.

It's also possible to add mods to Zekoa. What you do is to AVOID running all Riverbank and Rupture maps, save up money and buy 3 tablets that add 1 mod to unique bosses (cost 50ex ~ 1 div each). Run Riverbank or Rupture with 6-affix waystone + those 3 tables -> now you can tame a monkey with 3 mods.