What about, Pierce and Terry or Lee (if ATL is interested in either of those two, then the other one...Bass is probably too much to hope for) for pick 19 and 31.
Cleveland still adds their #1 pick and one second rounder to their roster, they clear 15mil off the cap next season for a run at a player who can opt out after next season, whoever that might be, and would definitely make the playoffs next year.
Boston gets to use $20mil of trade exception. $12mil and whoever we trade to ATL goes to Smith. Then we have a $8mil trade exception left to try and get a Kaman maybe? If not him then another big or save it.
Then you can try to get Schroeder and Giannis and maybe Withey in the second round.