The Heat have played their best when they play Bosh at 4 and a random large body at 5. Birdman works, but a better center wouldn't be terrible.
Really, though the Heat need several things. Not necessarily all of them at once, but a few good things would be:
a) A competent point guard. Chalmers is hot fucking garbage, and Cole is only good on limited minutes. I would NOT sign Melo or Love if I were Miami...I'd try and get Lowry if I were Miami. Dump Chalmers and some picks.
b) Solid bench players. Their bench other than Allen and Cole were awful in these playoffs. The bench is just too old. I'd look towards Meeks, Sefolosha, Jordan Hill, McBob...maybe even Mike Miller if they can swing that.
c) A true center. Doesn't need to be a starter, but someone who scores efficiently and can swallow up offensive boards. Monroe or Gortat would be great pickups.
Really, they SHOULD NOT sign another max SF/PF player. They need a starting 1, a good 6th man, and a center to play for Bosh so Bosh can play 4.
My fantasy starting 5 would be:
Lowry, Wade, Lebron, Bosh, Gortat