Hiya, Mary,
Woohoo! I'm excited for you! The Discovery Tower is my favorite building at the Disneyland Hotel, which is my favorite Disney Parks hotel. You are in for a wonderful treat!
I can tell you are sizing things up to make sure that everyone in your party will be as comfortable as possible in your Discovery Tower villa. I agree that it's best to set expectations appropriately. As you are aware, a 1 Bedroom Villa at the Disneyland Hotel features a king bed in the private bedroom and a main living area with a queen-size pull-down bed and a twin-size pull-down bed. The two pull-down beds are both standard sizes when considering the overall bed fixtures. The fixtures include casings that form the boxes around the beds when they are closed. The small amount of space taken up by those casings means that the mattresses themselves will be a few inches less than what you might typically expect in the dimension that folds down. For the twin-size bed, that means it would more comfortably accommodate Guests who are not as tall.
According to the Cast Members at the hotel front desk, the mattresses of the pull-down beds are Serta brand. To fit in their boxes in the closed position, they are not super tall mattresses. However, from my personal experience sleeping on a queen-size pull-down bed, the mattresses are wonderfully comfortable and offer a fantastic night's rest after a long day playing in the Theme Parks. I imagine the same can be said of the twin-size mattresses as well. Since they are pull-down beds, the mattresses can retain their regular shape instead of being folded and squished like sofa beds in many typical hotel rooms.
Tony's Tip: My family loves to dine at Palm Breeze Bar, located within the breezeway under the Discovery Tower. I highly recommend it, especially on nights when there are live musicians amplifying the already amazing vibe of this amazing restaurant and bar. I recommend the Cheese Fry Poutine and the Charcuterie Pizza. They also have the best mocktails around. When I dined there a few weeks ago, I thoroughly enjoyed the Fifty–Five–Fifty mocktail.
All in all, I'm very impressed by the accommodations at The Villas at Disneyland Hotel. My family enjoys staying there so much that we have become Disney Vacation Club members with The Villas at Disneyland Hotel as our home resort. We are thrilled to look forward to staying magical year after year at the Disneyland Resort. After staying there, perhaps you'll consider it too. Don't say you weren't warned!
Have a magical time, Mary,
~Tony