What sort of data are you looking to compress? Most of these "fast, small implementation" compressors don't crunch down common bytes into <8 bits, but instead f

What sort of data are you looking to compress? Most of these "fast, small implementation" compressors don't crunch down common bytes into <8 bits, but instead focus on encoding repeated multi-byte patterns only. (That's what "LZ" is). For LZ to compress well, you need a reasonably sized lookback buffer, plus a hash index of previously encountered patterns, so you might have trouble finding an LZ encoder that works with very little memory.