OK, let's not get all this popcorn wasted
.
I've decided to try a very simple circuit to get 10V output and to use the J211 transistor as a reference. This is a "budget" solution, as it requires only two good quality resistors (R1 and R2 and I've used 15ppm metal film for that, "padded" to the required value by some standard 100ppm/C resistors, so I should not expect much better performance than this value), cheap J211 JFET and an inexpensive INA133 chip connected as a gain 2 buffer with low tempco (~2ppm/C). Altogether is less than £10 in parts (resistors R3-R6 are internal for the INA133).
Here is the circuit which I've assembled on an old piece of a pcb:
And here is a 30-min run on the bench (vertical scale is 1ppm/div):
My estimate is that the temco around 23C is indeed about 10-15ppm/C. The power supply voltage variations from 12V to 28V create less than 2ppm/V change. The load regulation is better than 0.5ppm/mA (a conservative estimate, as a load current up to 5mA, sink or source, creates less than 1ppm voltage change). The supply current is about 2mA.
First R1 is selected for the lowest tempco and then R2 for 10V output voltage.
Cheers
Alex