When I go down the notes with falsetto, I reach a point where my voice cracks and I go into my normal chest voice.
My question is, is there a way to lower this 'threshold' before going into chest voice?
You'll probably find you don't have a single threshold between falsetto and chest/head voices, but instead these ranges overlap. Many singers work on extending the range of their head voice upwards to have a more full-bodied sound in a higher register.
Low-pitched falsetto is a bit of an oxymoron, I'm not entirely sure what you hope to achieve, but you'll find there's a point where your voice loses that thin, squeaky sound. You could try to sing 'at a whisper' to have a thinner kind of sound at lower registers, it's really a question of what you want to achieve.
The obvious workaround, of course, is just to sing a little higher when you want a falsetto sound. Raise the key a few steps, or skip up an octave if you can.