For the French and the Spanish fleets the preeminent source is an all but unobtainable book written by a Frenchman, Edouard Desbrieres. It was written in French around 1900 but an English translation was published around 1935. The translator's name was Constance Eastwick.
Desbrieres got hold of a report Villeneuve had penned before his sortie from Cadiz, going into significant detail as to the condition and crew quality of the entire squadron. If I recall correctly the report was found in the archives in Madrid. It never got any further.
In Desbrieres, Santissima Trinidad is described as being in very good condition. Formidable was a poor sailor, needing recoppering. Many of the ships are described as being indifferent sailers. The French Swiftsure is sprung, taking 6" of water an hour.
Several of the Spanish ships had been laid up in Cadiz for months, including S. Trinidad. They rounded up as many bodies as the could, including "herdsmen and beggers" to augment comparatively few sailors. There had been a smallpox outbreak, which had sorely depressed the local population. L'Aigle was described as having "good officers and crew." Rayo's crew, newly formed, was almost all soldiers.
Nelson's ship's crews were well drilled and cohesive with months at sea. Some of the Spanish ships had operated as crewed ships for a tiny march of hours. When the shooting started, some Spaniards crawled out the gunports to shelter on the unengaged sides of their ship.
I was able to find a translated copy in the USNA library. Its a 2 volume set. There has been one of the 2 volumes for sale from France for years. They want $1,750. USD
Desbrieres pulls no punches in his account of the global chess game from Toulon to the Caribbean, to Calder's fight, to Trafalgar. He all but accuses the French frigate captains of cowardice.
The Goodwin book is pretty good. Lots of line drawings. 30 odd pages of color illustrations. Not so strong on ship conditions on the day of battle.
Steer clear of Harbron. He's pretty superficial.
Hope this helps.