I've just taken a look at the current deck.
get rid of
Rhonas's Monument. you usually won't cast enough creatures to make use of the cast effect. besides that, you have just 7 targets for the cost reduction, so it won't really ramp.
Oketra's Monument is way better, because the cast effect synergizes well with najeela.
Shard Convergence would also be a possible option. it isn't that cheap to play and "only" gives you the lands on the hand, but it makes sure that you've got all colors. Besides that, you are just limited for land types, so it will somewhat
scale up if you improve your land base (e.g. battle lands).
Joiner Adept is another budget card that could help with color fixing, as well as
Chromatic Lantern, even if the lantern is a little more expensive.
Ash Barrens is, at least for me, a little better than
evolving wilds, since you can just play it as colorless lands later on. the cycling cost first seem to make it worse, but the fact that you can use the land you fetch afterwards brings it on pair. the only situation where
evolving wilds is strict better is the turn 1 lant drop
If you want to play combo,
Druids' Repository would be a possible option. once you get 5 warriors able to attack, you're able to generate endless combat steps.
besides that, here is my najeela deck. It won't help you much with the mana base, because it's build on a higher budget, but maybe you'll notice something else that catches your eye. My personal restriction was warrior tribe (with
Dryad of the Ilysian Grove as only exception because of it's damn good mana fixing abilities).
https://deckstats.net/decks/112190/1047892-najeela-warrior-tribe/