Because we have only 1 weapon, it need a ability to kill fastest and strongest microbes.
Frostthrower have nice firerate, burn and bounce from the start.

Stapler - Technically reduces hp of most enemies by 25%
Rime - play style of this build means constant shoting, so faster cooling be not worst chose.
Leaf - make thrower-like weapon little better, because it faster reach end of the screen. (And you can freely grab some speed reduced upgrades)
Pot - worse when Leaf in a start, but can actually increase your damage.

Universal staff:
Mirror and Defibrillator - Help you live longer.
Eraser - If you have empty perk slot (Sieve - is practically better, but harder to unlock.)
Mushroom - Can kill biggest enemies, but only once per wave, so grab if you like it .

For more hardcore buddies:
Calculator - 25% damage increase, but you need to dont make mistakes.
Worm - very bad on first waves, but in the end of this build dont actually decrease anything.
Turbine - give you nice cooling, but feel like knife juggling.

Weapon upgrades:
ONLY 1 increase crit chance. (Due how burn work)
1 or 2 range increase. (after all calculation in need to be ~300%)
Sticky - great thing with bounce, but quite rare.
1 size increase.
As many accuracy reduce as you can. (Because it does not needed)

Turret upgrates:
Pierce, Bounce and Sticky(if you have weapon upgrade) - all of them good.
More firerate for weapons with A DNA
Heat reduce per elimination - if you dont grab Rime.