OK just got the badge of the day - start doing bubbles in a spiral to keep the enemies easy. Once you have a solid white circle you cannot upgrade further - I wasn't sure about this but after clearing around 100 more bubbles I had no more upgrades. at this point it is better to head straight out - I met the boss 16 bubbles out from my cleared spiral. I believe he only appears if you are fully upgraded. There some bubbles with enemies that are just a big blob of bubbles that split into smaller unarmed ships - I recommend not killing these outright as they could be 'farmed' for bubbles if you are weakened (take a few bubbles then leave and re-enter the bubble). if this helps plus the comment.
 "Bubble Tanks"){kind=icon}
 "Takeover"){kind=icon}