OK, thanks to you Ladies, I went out and got a key pendant/chain for my Mother's Day gift! My poor son almost keeled over when we walked into Tiffany's for my gift (he's only 15, no job), but I told him not to worry, he could just contribute whatever he was able to afford!
Originally, I wanted the silver oval key in the extra-large size, but it was just way too big (I'm 5'5", slim). It only came in the small or XL, so I tried the vintage oval instead in the 2" size on a 16" chain (which is usually too short for me, but it worked really well with the size of the key), and fell in love! I got it with the oval link chain.
Thanks for the tip Ladies!!!