Learn French: C'est le mode de vie dont nous avons besoin.

In French, the expression for "to need" is avoir besoin de. When a relative pronoun connects back to a noun that requires the preposition de, French uses the pronoun dont instead of que. Because we say avoir besoin de quelque chose, we must use dont to link the need back to le mode de vie.

Could I say "C'est le mode de vie que nous avons besoin de"?

No, you can never leave a preposition dangling at the end of a clause in French like you often do in English. Furthermore, the word dont already includes the grammatical function of de, so adding de at the end of the sentence is redundant and incorrect.

Why is it C'est instead of Il est here?

When you are identifying a specific thing using a noun phrase (a noun introduced by an article like le, la, un, or une), you use c'est. Because we are saying "It is the lifestyle" (c'est le mode de vie), we must use c'est. You would typically use il est when it is followed by an adjective alone.

Can I use style de vie instead of mode de vie?

Both translate to "lifestyle" and are understood to mean the same thing. However, mode de vie is the much more traditional and common expression in French to describe everyday habits, living conditions, and routines.