Sounds like you're not kneejerk against metric, I'd just go ahead and buy some metric tools. Imperial/metric tape measures are very inexpensive on Amazon, beyond that I have a metric caliper and use the metric rule on my table saw, that's all it takes to stay in the land of easy math.

Look into using dictionaries. You can even use tuples as the key so:

conversions = {
    ("meter", "yard"): (m, b),
}

This is just an idea and not sure exactly what you are looking for. Another option could be converting all metric values to the same unit and then running 1 function to convert to imperial...just brainstorming.