Your tail lights area already LED, and do not have a user-replaceable bulb. Your tail lights are the 3 light tube things. Brake lights are regular halogen bulbs though.
Aftermarket LED replacement bulbs tend not to be very bright unless you shell out $$$ for the super bright ones.
I think a better option would be to save up for LCI tail conversion.
AW/Terra | ZSP | ZPP | ZCW | iDrive | CA
Mods: BC BR coilovers | Blacklines | M-tech rear | dual exhaust | M3 steering wheel | BMW SSK | ZHP shift knob | High-kick CF spoiler | NBT Retrofit
M3 front control arms | M3 rear guide rods | Manzo rear toe and camber links | Monroe rear shock mounts | Varrstoen ES1 19x9.5+20 Front, 19x11+25 rear