Metric adoption doesn't have to be all or nothing - that would be intimidating, and there can be real barriers to using metric today (such as with speed limit signs). Choose an area where you can successfully use metric - switch your weather apps to Celsius, log kilometers for running or biking, or flip your scale to kilograms. If you are able to lead a switch to metric at work that is even better - you're bringing a team along with you.
With a few weeks of practice, you'll have a real win under your belt. You'll see 12 °C and know what to wear, or you'll think "tomorrow I'll do an extra two kilometers."
As much as possible, don't try to do conversions back and forth between metric and non-metric.
Just forget about the old units. If you weigh yourself and find that you are 75 kilograms, then now you have an idea of what 75 kg means. You don't need to know what that is in pounds - in fact, thinking about the pounds equivalent will just make things more confusing.
Next, you can weigh your kids, or a heavy backpack, or look at the product label that shows the weight of the contents. Now you have some reference points to build a mental framework for what a kilogram means. It doesn't mean a certain number of pounds; it means weight that you can feel with your hands.
You're going to have plenty of moments where you don't know the metric measurement of something, or you can't immediately picture a number you read or hear. That's normal - it takes some time.
You don't need to get it exactly right. If you guess that a glass holds 250 milliliters of water and it really holds 200, will anyone notice? Probably not.
Most people are worse at estimating than they realize. You may not be able to picture "150 meters" very well, but most people can't really picture "500 feet" either. In either system, practice helps - and you may simply have more practice with feet.
