So I'm aware that in ~14th century most of the medieval armies were made up of either nobles or levied freeman/peasants, however I can't find any reference to private soldiers or guards of nobles.
Who would these nobles use as guards for their house or when travelling? I'm assuming that they would have a small number of armed men for general purposes and I keep seeing references suggesting it was the case but nothing definite. I know wealthy nobles and royalty employed knights to work in their household but what about lower nobility who can't afford such expenses, such as landed knights?
Your view of how medieval armies were composed is largely wrong, particularly if you are refering to the 14th century, as even before the 11th, armies were already much more specialized than that.
Most armies were composed of relatively professional soldiers, who were recruited throughout the country, as well as mercenaries hired for the duration of the campaign. These men would serve as garrison (or bodyguards, you might consider) in the places they were hired.
Sources
Maurice Keen, Medieval Warfare: A History. Oxford University Press
Rodney Hilton, The English Rising of 1381. Cambridge University Press. (In this book, Hilton argues that peasants had an almost null participation in war during the Middle Ages, with the exception of a few specific cases).