Hi,
You could alternatively keep the 75watt and get a rheostat to dim it down - that gives you a little more control over just relying on a set wattage.
And yes I think the digital thermometers/hydrometers with the probes are the way to go - it's easy to put the probes of those inside the hides to see what temperatures the snake is actually being exposed to while your adjusting your thermostat.
dr del