Booker/Klobuchar seems like the likeliest single option, but at least one person on the ticket will be someone who is deeply non-obvious right now; the last election to lack someone like that was 2004. (Palin, Ryan, and Trump -- and arguably Obama -- were deeply non-obvious four years in advance).
Why does anyone think Booker has any better chance than Kasich did...?
Identity politics will favor him strongly, plus his wing of the Democratic Party is much stronger than Kasich's wing of the Republican Party.
