"Based on" instead of "based off of"
Solution 1:
The former is certainly preferable in UK English, formal or otherwise, whereas the latter is a style usually heard in conversational American English.
Solution 2:
I checked in the Corpus of Contemporary American English and there are only 7 instances when based off of is used, limited to spoken style. On the other hand, based on occurs with very high frequency in all sorts of discourse, particularly academic but also spoken.