You can get both digital oil and coolant temps on your dash for ~$65. Cyberdyne sells a line of digital gauges, an example of which is here, even if this price isn’t that good. http://www.jegs.com/i/Cyberdyne/280/A220E260Y/10002/-1
The problem with digital gauges is they are slow to read. But if you’re especially anal you could could get both by installing a small 2 1/8th digital gauge to supplement both your pre-existing big 2 5/8th analog oil temp gauge and your big 2 5/8 coolant temp gauge. Here’s how to do it…
Buy the Cyberdyne temp gauge, being sure to get one that comes with the sender. Then buy an extra sender. For the gauge I linked, the extra sender part # is SENSS6E. Plumb both senders into appropriate places, and then bring the wires to the dashboard via a double-pole switch. Then the switch will allow the single small gauge to handle both senders. If you’re feeling anal about oil temps, flick the switch to “oil” and so on for coolant.