One of the best thimbles for quilters with long fingernails is the Roxanne thimble. It is expensive, but it comes in many different sizes so you can get one that fits, and it will last forever. There's also a Clover (?) thimble that is lightweight bronze that also has a fingernail hole.
You may be able to get the plastic thimble to fit better by warming it. I've been known to slip a little batting in the thimble to get a better fit.
For a needle, I prefer Richard Hemmings or John James, in size 11. I like a smaller needle, but I've been hand quilting for a long time. I suggest trying different needles to see which one works best for you.
The Thimblelady has her own way of quilting, which defies conventional wisdom and uses long thin needles and her own thimble - if you go to her website,
www.thimblelady.com, she has them for sale. The secret is that she keeps the sandwich very very loose in the hoop. She also sells an inexpensive plastic version of her thimble. Her work is phenomenal!
Janet