Those are good suggestions. Of the two, I'd probably lean towards Kelestia, since it is roughly equidistant from Jaiman and Emer, whereas Thuul is far from Jaiman.
rereading the master atlas ...
Kelestia would be some sort of mostly stone/bronze age setting with the Raven Queen as only adversary.
Thuul on the other side is interesting ... almost like europe including mediterrenian seas and northern africa !
Isra in Kelestia is TL4, and parts of Verya are up to TL3. But the rest is officially TL1-2, which is more primitive, technologically speaking, than most of Jaiman.
However, technological bronze age does not mean non-civilised (most of heroic and classic Greece is bronze age, as are Egypt and most famous middle eastern pre-islamic civilisations). On Emer, almost all of Tai-Emer (Pochantos and Lankanôk) is TL2-3, Vajaar is 2-3, the Rhiani and Shynsari are TL2, as are Quon and Ahnasan. Basically, more than half of Emer is TL2 or at most 3. And no one ever said that Emer was dull
(and if you check Thuul, the situation is not much better).
Kelestia is also close to both Jaiman and Emer, and also close to Gaalt (I'm not including Iyxia, because it is mostly inaccessible), and most of southern Kelestia was once part of Voriig Kye's Dragon Kingdom, which is a major plot point of sorts.
In terms of integration with the existing books, Kelestia is the better choice.
(but as I said, I am partial to Thuul. It's even more a continent of contrasts than Emer is, has unmistakable features - including the Pillar of the Gods, major plot points in the Alliance war against Vashaan colonies, one of the Ahrenreth's Secrets... and the racial mix is all over the place).