I'd treat a boomerang as a non-weapon, unable to even serve as an improvised weapon.
I know that's not the answer you're looking for, so how about this:
Boomerang
Martial ranged weapon
75 gp
1d6 bludgeoning damage
Returning (range 30/120), light
Returning: This weapon returns to you after being thrown (on a hit or miss). Because of the time required to catch it, you can throw it only once when you use an action, bonus action, or reaction to throw it, regardless of the number of attacks you can normally make.
In general, I'd agree with a fair amount of that.
I think 1d6 is more appropriate for a bladed boomerang (dealing slashing damage) or for a boomerang reinforced and weighted with small metal plates. I'd go with 1d4 for a more standard blunt, wooden boomerang.
I think the 75 gp cost is a bit high. I'd probably go with 50 for the 1d6 bladed or weighted version, and 25 for the standard wooden version.
I like the range you've given it.
I mostly like the returning property you gave it. However, I'd require an object interaction to catch the returning boomerang. If you used that up already, say to draw the boomerang on the turn you threw it, then you'd have to blow your bonus action to catch it. I'd also stipulate when it returns to you. I'd probably go with the end of your turn, but I can see a valid argument for the start of your next turn.
I think the determination of whether it's a martial or exotic weapon should probably depend on culture. Just as a boomerang would be an exotic weapon in Europe and a much less exotic weapon in Australia, so I could see it being an exotic weapon in some parts of the game world and a martial weapon in others.
I also wouldn't have a problem with the simultaneous existence of a cheapo, 1d4, returns only on a miss, simple ranged weapon version used by commoners to hunt small game (i.e. the real-world usage).