I find that digging into the words help. In your case, you're mixing them up because they are indeed related! Somebody who's costaud has strong côtes (according to the CNRTL, they are not 100% sure either).
In my case with Chinese words I learnt to write them so I'd distinguish 我找钱 much more clearly, but I still get the odd mistake like when I confused 午(noon) next to a horse for 牛 (cow)... I was very confused as to why the horse was labeled as cow. But yeah, the general idea is to have more data from more senses to sort the words better in my brain.
Their shape, their sound, the way to write them (physical movements), a picture of what they represent, an anecdote tied to the word, or in this case to learning the word, etc.

