Ummm... Maybe you should try
miwa or
ayaka?
If you like strong voice and lyrics like Van Tomiko or alan, I recommend ayaka so much
But if you like some cute voice like Ai Otsuka, I recommend miwa
I give suggestions live videos, because their voice in live and CDs is 99% exactly the same
miwa - don't cry anymore
ayaka - Te wo Tsunagou