The Bees are ninth in the Championship, 13 points behind Saturday's opponents Fulham with two games left to play.
They need two more points to better last season's tally of 65, but Smith believes they will need new recruits if they are to ever reach the play-offs.
"At the moment we're stockpiling B-team players into our squad to fill it up on a matchday," he told BBC Radio London.
Despite Brentford's small squad, the west London club are on course for their third consecutive top-10 finish in the Championship since being promoted from League One in 2014.
A run of five wins in their last seven league games has propelled the Bees up the table, but despite the club's consistency, Smith is eager to push on and aim higher.
He said: "While it's great that the B-team players are getting experience - and it's something we want to do - if we want to challenge for a top six spot we have to add more quality to that.
"We'll certainly be looking to do that [before next season]."
After their 3-1 win over rivals QPR, Brentford finish their Championship campaign with a trip to Craven Cottage to face Fulham before a home game against relegation-threatened Blackburn.
Brentford manager Dean Smith says he needs more players if the club want to break into the top six next season.