I recommend starting with Ian Mortimer, The Time Traveller's Guide to Fourteenth-Century England. It's not an academic book, but that makes it more readable (heh) and it is very well-sourced.

The Greenwood Press "Daily Life" series has a few medieval volumes that are good: Daily Life in Medieval Europe, Daily Life During the Black Death, Daily Life in Chaucer's England. Additionally, not from GP, there is Daily Life in the Medieval Islamic World which I would recommend as well!

Barbara Hanawalt, The Ties That Bound, is a really good one to read if you're interested in peasant life. If you're focusing on nobility and want a better grounding there, it would help to know the vibe you are going for--a more 'Dark Ages' one or a Game of Thrones/borderline early modern one.

But in general, you have a couple of options to think about. The Middle Ages span 1000 years and 3 continents, generally speaking (tabling the debate about whether we can talk about medieval Americas for now). So you can either zoom in on one particular time and set of contexts--assuming your characters travel--or you can mix and match from different times and places because you're making a fantasy world so you get to have all the "cool parts." Totally up to you! Just something to think about.

On which note about travel: Jean Verdon, Travel in the Middle Ages, would be worth your while if that's a central part of your story.

And finally, one thing to consider is religion. Even if individual people weren't always deeply spiritual, religion drenched medieval life in a way that's almost impossible for us in the modern West to imagine. If this is an aspect of medieval life you're willing to try to capture, Kevin Madigan, Medieval Christianity, and People's History of Christianity: Medieval Christianity would both work. Since they are topical-by-chapter, you could pick the ones that seem relevant.

...But if all this seems overwhelming, just pick up Mortimer. :)

In addition to the other recommendations, I would suggest the works of Joseph and Francis Gies, specifically their "Life in a Medieval..." series, which covers villages, towns and castles in mid-13th century France and should be a good compliment to Ian Mortimer, and Cathedral, Forge and Waterwheel, which provides an excellent introduction to and summary of medieval technology and its development.

In terms of military reading, I highly recommend Michael Prestwich's Armies and Warfare in the Middle Ages as it covers every aspect of a campaign. It is only focused on England, but aspects such as intelligence, logistics and finance would be relatively similar across Europe (though the latter would be more hodge podge in places like France). A good supplement would be Ian Heath's Armies of Feudal Europe and Armies of the Middle Ages, which cover most of Europe and provide basic information on recruitment and organisation, as well as miscellaneous information on tactics and equipment. Probably most useful to you would be the many drawings of different troop types.