First of all: Thank you very much for your advices!
Yeah, I too thought that the creatures need trample, however the options are slim. I thought about adding Nylea too, however in this deck she won't be a creature most of times - which means it's just an expensive enchantment for 4 mana. On the other hand you can use her as "mana sink" as well.
About Molimo: Even though this deck conain's a lot of ramp, I think Molimo is still too expensive and can easily be removed. On top of that he just grants himself trample; not the other creatures.
About Baru: Yeah, I haven't thought about this creature and it could really enhance the deck.
I'll consider your advices and I'll probably add one of the mentioned creatures above or some other trample enabler.