The book on the Doniphon campaign is about one expedition that travelled from Missouri, to Bent's Fort, to Santa Fe and then down into Chihuahua, where they lived off the land and went native after a fashion. I put it up there with the Anabasis among stories of great military wandering books.
There was an excellent collection of pieces by Mexicans about the war which was published by either UT or A&M press some years ago called The View From Chapultapec. It collects a number of different opinions from Mexican authors and offers some very good insight.
One, for example, offered the opinion that the Americans were successful because Mexican nationalism was not that strong. When Americans needed food or mules, etc, there was always some Mexicans happy to sell. Compare that to Texas during the Runaway Scrape where they burned or killed what they could not tote off.
Overall, I think the Eisenhower book is the best starter on the war. Too bad there is no good biography of Polk to accompany it. It was his war and the best understanding of why it was waged can be found in his diaries but they are too long to burden a non professional with.
He wanted California to go with Washington, which he threatened England with war over.
The English compromised, as did Polk. The Mexicans would not and the US got everything but had to fight an unnecessary war to get it.
By the way, the building the Texas Rangers stayed in while in Mexico City is still there on Doncelles Street, near the Zocalo.