"I'm always confident because we did some good business but everybody knows and the board knows the importance of those two signings."
One of the names linked with Everton is wantaway Chelsea striker Costa, but when quizzed if he could arrive at Goodison Park before Thursday's Deadline Day, Koeman kept his cards close to his chest.
"I don't know [about Costa]. We are looking at players who are available and if we sign somebody, it is somebody who makes the team better," the Dutchman added.
"I don't speak about names, about players. It is the media who is talking about Costa or other players, but we are looking and we do our job and hopefully, we will arrange it [a striker to arrive] for next week."
Barkley and Kevin Mirallas were both absent from Everton's match day 18 and have also been subject to transfer talk, with Koeman giving updates on their current positions at the club.
"Mirallas was out because he is struggling to deal with moments in the season and with disappointments. Everybody can be disappointed but I expect from everybody to be part of the team and if somebody is showing that his attitude is not the same, I make decisions," he said.
"Until today, yes [Barkley is staying at Everton], because we don't have any offer on the table for Ross."http://www.skysports.com/football/news/11671/11009069/everton-manager-ronald-koeman-coy-on-diego-costa-link-but-wants-to-sign-two-more-players