"I promised the current set of lads they would get every opportunity to prove themselves in the Championship," Johnson told BBC Sport.
"But I am still looking to get in about three or four players because our squad is quite small.
"The chairman knows I will only bring in a player if he's value for money."
Meanwhile, Johnson said he was looking forward to taking his side to Latvia on a pre-season tour - a country he knows a lot about.
 | They've also got lovely white sandy beaches Johnson on Latvia |
The 51-year-old coached the national side for two years between 1999 and 2001.
"I'm hoping the trip will prove a useful experience for the guys before the start of the new season," he said.
"We're playing the top teams over there, including Skonto Riga. The training facilities are great and the stadiums are top class.
"They've also got lovely white sandy beaches so the players can relax when they get over there.
"It's not really a team-bonding exercise, because the team are pretty bonded anyway."
Looking ahead to Bristol City's first season in the second tier of English football in nine years, Johnson believed that the usual suspects will be challenging for promotion to the Premiership.
"Sides like Charlton and Sheffield United have got the best chance of going back up because they will benefit from parachute payments over the next few years," he added.
"It's a fact of life that the relegated teams will begin the new season as favourites for promotion. It's up to teams like us to challenge them."