Your uses of "based on/according to" are generally correct, but you have some other errors in the sentences.
1. I make a decision [or make decisions] based on/according to the need [or needs] of the situation.
2. I make a decision based on/according to the situation and its need. [The possessive "its" does not have an apostrophe]
3. I make a decision that suits the need [or decisions that suit the needs] of the situation and act accordingly.
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