You also may have been served a white half runner. These are my favorite green bean for all the reasons you listed! Yes, they have strings and are more work to process but worth it to me.
I also enjoy the rattlesnake bean, too. Many of the commercial white half runners have been corrupted and are now tough. I don't recommend ordering those from the big seed companies. The old fashioned white half runners are hard to find. Bill Best has been collecting/growing these for years.
https://www.heirlooms.org
His beans are also $6 a pack. I'm trying two new ones this year. So far I have been able to save seeds on beans where I garden but the bug load can be pretty bad here, too. Good luck on your quest.