In their first season back in the Premier League, the Hammers have excelled and are on course for a top-half finish, despite boss Sam Allardyce coming under much scrutiny earlier in the season.
And with the club due to move into the Olympic Stadium in 2016, the future looks even more promising for the east London club.
"Our planning has already started to make sure next season is even better," Sullivan told The Sun.
"A crucial factor will be recruiting the right players in the right positions."
Goals have been hard to come by on their return to the top flight, and leading scorer Andy Carroll looks unlikely to make his switch to Upton Park permanent due to his excessive wage demands.
Sullivan knows that should Carroll return to his parent club Liverpool, then he and boss Allardyce must make the acquisition of a striker their priority.
"We want to bring in at least one proven goalscorer to bolster our attack," he added.
"We want to strengthen the squad and provide manager Sam Allardyce with greater options and variety."