Struggling with mass removal is kind of a given in mono green. Especially with only instants and sorceries. You can't really run something like
The Great Aurora, because your opponents will probably benefit more. You can't run
Bane of Progress because it's a creature, and
Nevinyrral's Disk because it's an artifact. There really aren't options in green for mass creature removal of non-fliers.
You might consider running more spells that give +1/+1 counters instead of temporary boosts. That would at least allow you to go tall with Toski. Aside from that, this seems like a particularly difficult build challenge, given that Toski is much better in swarm decks and a lot of green voltron is locked behind permanents.
EDIT:
Endless Swarm could be funny jank though for a "no permanents" swarm deck.