First, you're not the only one who has difficulty. It's not your imagination, and it's not just about age. It IS a confusing subject, and it changes all the time.
Here's Consumer Cellular's page on international roaming: https://www.consumercellular.com/Help/international-rates/roaming
Looking at Consumer Cellular's website, it seems their plans and phones now do roam in the UK. Your cost is $0.30 per talk minute, $0.10 per text message, and $0.25 per MB of data usage.
What that means in lay terms is: The occasional call or text is a good deal. A lot of calls or texts will start to add up fast. And using data will break you.
If all you want to do is make a few short calls to taxis or Airbnb's, you're set. You do have to turn on international service, and they recommend that you do this two weeks before travel, so do this today by calling (888) 345-5509.
You can also use your phone on Wi-Fi at no charge, or at only the charge for the Wi-Fi itself (for instance, my Edinburgh Travelodge Hotel is charging £3 per day for Wi-Fi).
If you want to use a phone for anything other than calls, texts, and Wi-Fi, let us know, so we can figure out other options for you.
You can program numbers in your phone now so they will work with your phone when you're in the UK. Program in the number as +44, then the area code (omitting the initial zero), then the number. For instance, my Glasgow hotel's front desk was 0141 357 5155. So, it goes into my phone as +44 141 357 5155 (the phone will put in spaces or dashes automatically). To get the plus sign, just press and hold the zero. Once a number is entered this way, it will dial correctly from wherever you are, so be careful not to dial it from the US, as you'll have to pay Consumer Cellular's international rates.