Low power hysteresis circuit

[procnias]

Hello,
I am a biologist working on hummingbird behavior (I bet you don't get that one everyday) and I am designing a solar re-charged radio transmitter to track the birds' movements. As I am severely weight-restricted I cannot place enough solar cells on the birds to keep the tags fully charged. So my only option is to find a way to charge the tag up with the transmitter off until the battery reaches a certain voltage, then to discharge to a lower level than the initial trigger voltage (hysteresis). I've come up with a thyristor circuit (attached) that will trigger the transmitter at ~3V, then stay on until it reaches ~1.2V at which point it turns off again to allow the battery to recharge (I can explain the attached circuit further if needed). Unfortunately, by using BJTs I get a 0.6 - 0.7 V drop, and given that the transmitter operates only from 1.2-3 V, this is just too much of a drop.
Can any of you tech-savvy people out there think of a hysteresis circuit (Schmitt trigger, thyristor, bistable latch) that 1) has a much smaller (or essentially no) voltage drop (maybe using CMOS?), 3) is fully controllable so that I can trigger at a high voltage and untrigger at a lower voltage, and 3) uses no more than 4-6 transistors and no op-amps; the tag must ultimately be less than 3 x 3 x 0.5 mm, so I can only use SOT-883 size transistors. If you can point me in the right direction I will be eternally grateful!
Thanks!