[mellody]

If you ask about 80s and 90s idols, then you should listen to Matsuyoya Yumi, Iwasaki Hiromi, Yamaguchi Momoe and Nakajima Miyuki.
I think you can start from their best album, if not, try their early release, 1st or 2nd album most of time sounds awesome.

As for new artists, since I read Tsukiko Amano in your list, have you heard of Nana Kitade?
I really really like all of her music, since she has unique voice, maybe you will like it too.

The rest that I can think of are Kalafina and moumoon.
Kalafina is neoclassical pop group, they tend to do many harmonization, so amazing.
While moumoon has really versatile genre, though mostly pop but their music is just so diverse but very enjoyable.