How do you Synthesise a Fatty Acid Amide?
You are perfectly right on that you need to convert the carboxylic acid to a more reactive species to eventually obtain the amide!

Playing with the pH will not help: 


under acidic conditions, the amine is protonated and therefore unreactive  
under alkaline conditions, the acid is deprotonated and the carboxylate won't react at all


The Schotten-Baumann reaction of fatty acids with $\ce{SOCl2}$ will probably work fine: 


reflux 1 mol of the acid with 1.5 mol of thionyl chloride   
dIstill the remaining thionyl chloride off
purify the fatty acid chloride by distillation in vacuum. Note that the bp of stearoyl chloride is about 175 °C at 2 mm Hg!


This is quite some work to obtain a fatty acid derivative that eventually reacts with an amine!

Wouldn't it be much more convenient to form the amide in a one-pot reaction, possibly at room temperature, by activating the carboxylic acid  in situ? 

(In situ means: at the same spot, without isolating the reactive intermediate.)

There's a large number of coupling reagents available, such as   


carbodiimides like DCC (dicyclohexylcarbodiimide)  
$1H$-benzotriazoles
chloro-substituted triazines


Eric Valeur and Mark Bradley published a critical review titled Amide bond formation: beyond the myth of coupling reagents, in Chem. Soc. Rev., 2009, 38, 606-631 (DOI) on the topic.