Here are some authors that I've tried and can recommend as very good:

And a few other authors I've seen mentioned as similar to Stewart but haven't read:
Victoria Holt, Dorothy Eden, Phyllis Whitney
Anyone have any other suggestions?
But one convention of the mainstream of adventure fiction I have kept right through my novels, the convention that the good ends happily, the bad unhappily. "That is what fiction means," said Oscar Wilde. We can laugh at it, but it is sound tradition. A complicated plot rounded off with the reader's imagination projected willingly into the future, is a deeply satisfying reading experience. It is also much more difficult to write effectively than the unresolved or the tragic ending.
With Thunder on the Right, I tried a technical change of approach, from first person to third. I had dropped naturally, without calculation, into the first person ... but now thought it right to experiment. Of course writing in the first person has certain drawbacks, especially in "danger" and "suspense" situations--certain elements of surprise are cut out, the viewpoint is limited, and direct action is also limited to scenes where the protagonist is present--but for me the advantages far outweigh the losses. The gain in vividness, personal involvement and identification is immense.
In Thunder on the Right, with the third-person approach, I found I had more freedom of action and viewpoint, but in my next novel, Nine Coaches Waiting, went back with a kind of relief to the first person, and have used it ever since.
---"Teller of Tales" in The Writer, Vol 83, p.11