My DS wore a lifejacket at WL and AKL when he was around 4 or 5. Not sure about sliding with a 2.5 year old unless you have mommy and daddy at the top and bottom respectively waiting.
The mildest slide we've had was POFQ, which may be the best for a 2.5 year old.
POR, WL, and AKL were fairly mild. CSR is a bit higher and longer.
SAB has an area with a slide for little ones.