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The polymorph section of the core rulebook says that if the new form has an ability, and the polymorph spell grants a lesser ability of the same type, you get the lesser version.
A stricter interpretation might hold that it can only be numerically lesser — ie, the new form has blindsense 120' and Beast Shape IV only grants 60', so you get 60'. However, since blindsight is explicitly described as a superior version of blindsense, it's completely reasonable to grant blindsense to a polymorph form that normally has blindsight.
Also, if you're worried about underwhelming damage while in ooze form... just turn into a carnivorous crystal (Bestiary 3) whose natural weapon is a 7d8 slam attack with a critical threat range of 18-20.