One thing I've realised about this project, is that there is currently no indication for when a value is negative. The popular use for Nixies is to make clocks, so there is no use for this sort of indicator. A quick search found me three complimentary Nixie beauties - the IN-19A, IN-19B and IN-19V. The IN-19V is going to be the most used for value indication, as it has all the common symbols. The others are additional scientific indicators, and I'm tempted to get the lot. These are all visually and dimensionally compatible with my IN-14 tubes.

I'm now uncertain if the existing HV module is going to be able to supply enough current for the extra tubes.