Help with Amplifier and speaker

[gpxfiles77]

Hi,
I have a project that I need to do and was hoping I could find some help here.
I have a PlantronicsPro bluetooth mono headset that does not have sufficient volume.

I would like to remove the speaker and clip the positive and negative speaker wires. Then I would like to connect the speakers wires to a Class A amplifier, perhaps rated at 500mw with a supply voltage of 3.7 volt or around there. I would like to connect the amplifier to an approprate full range output speaker rated at at least 500mw.

Questions-
What class A amp can I use, specifically what model from Digikey or similar? I do not know the typical mw rating of most small amplifiers and small speakers so for now I am guessing 500 mw. The frequency range needs to be as flat and wide as possible, I need the high frequencies to be amplified, not the lows.

What speaker could I use? It needs to be small, maybe 5mm in diameter or less. It needs to have a good flat frequency repsonse over a large frequency range even though the bluetooth built in amp is likely a narrow range.

I would really appreciate any help on the above questions.