Cradle is a great regional book but its main focus is neither malaysian or Nyonya.
Here are some books (not sure of current availability) that might fill the bill
Makan - Lah - Carol Selvah Rajah's excellent Malaysian book, originally published in Australia
Rasa Malaysia, by Betty Yew Published by Times Books , Singapore and KL - very comprehensive and presents Malaysian Recipes state by state. Ingredients might be a challenge as with some of these books which intended for an in-region audience
Penang Nyonya Cuisine, by Cecelia Tan published by Times Books - I see she also has a mini Nyonya book out which is currently available
More from the Singapore side
by Terry Tan - Straits Chinese Cookbook (an older book) and Shiok! by Terry and Christoper Tan (a new Periplus book by him)
books by Mrs Leong Yee Soo - the best of Singapore cooking, and Festive Recipes, the Best of Singapore's Recipes - I have not yet cooked from these but she is authoritative on the Straits Nyonya cuisine
The Periplus Malaysian and Singapore books are also quite good but, like Shiok in a 2pg and pics per recipe format, dont set out to be comprehensive.
How serious are you about this? Are their particular specialties/regional dishes you are looking for? for example, there is at least one Penang Cookbook out there. Would Singapore Nonya cooking do? Terry Tan and Mrs. Lee both have good books out in this area.
There ae a number of books available, I have a few but it would help to know more about what you are looking for.
Or you might want to get started at the KL Star Online's recipe site