Some cards I found might work well for your main setup:

groundswell - not a game ender punch like untamed might, but 1 mana to get a possible +4/+4 is very efficient, next would be giant growth and vines of vastwood.  vines of vastwood will give some protection too.

Those efficient greens are awesome with ichorclaw myr due to the fact that the opponent more than likely will take 1 poison instead of kill of a 3/3.  then for 1 mana, you can get a possible 5 poison counters in 1 hit

Contagion Engine is nice, but contagion clasp might be a enough along with throne of geth, replace the contagion Engine with Livewire Lash - cast any one of the many instants on livewire lash equiped creature with infect, and you will do  as many poison counters for about 3 less mana, except not proliferating across all creatures.  or get rid of throne of geth and put in a livewire lash.

Whispersilk Cloak would be a good one to squeeze in there too possibly...nothing like an unblockable shroud infect creature.

Plague stingers are cheap and nasty, possibly add 2 more and pop off a cystbearer and maybe 1 tangle angler, that would improve your mana curve leaving you more mana later on for contagion clasp or equips.

just some thoughts to toss around, we will have to play test the deck soon.