In "The Geometry of Iterated Loop Spaces", May shows that any monad that is coming from an operad may be "whiskered", so that the unit map becomes a closed cofibration. The ability to do this is vital to constructing simplicial resolutions. In particular, it guarantees that the bar resolution $B_\bullet(T, T, X)$ is a proper (or good, in Segal's terminology) simplicial space.
I am wondering in what generality this can be done. Given a topological monad $T$, when can I find a monad $T'$ whose unit is a closed cofibration, along with a morphism of monads $T' \rightarrow T$ inducing homotopy equivalences $T'(X) \simeq T(X)$ for all spaces $X$?