what clause来自一个主系表结构的句子(主语+系词+表语):
这个句子可以是:
(1)the real bliss in this world to me is my son.
也可以是:
(2) my son is the real bliss in this world to me.
所以用what来替代了my son之后然后提前到句首来lead this clause,就可以是:
what the real bliss in this world to me is.
or:
what is the real bliss in this world to me.
to me 的位置我觉得可以灵活,所以你上面说的三个用法我觉得句法上都对。具体哪个更好一些,我想跟想强调的方面不一样有关,和个人说话习惯有关,得问问native speaker了。