"Whether we're going to say Carlos is going to play first base or Brett's going to play first base or whatever, let's let these guys go play and continue to work," Mills said. "We're keeping an open mind with those guys, and that's going to help as we go into Spring Training."
The Astros acquired Wallace from the Blue Jays in July in a secondary deal of the Roy Oswalt trade with the Phillies, and anointed him their starting first baseman when Berkman was dealt to the Yankees only hours later.
Wallace, an accomplished hitter in the Minor Leagues, hit just .222 with two homers and 13 RBIs in 51 games for the Astros. He wound up splitting time at first base in September with Lee, who's been the team's starting left fielder since 2007 but is a defensive liability.
"Brett Wallace is going to be a good Major League player, and we saw that at times last [season]," Mills said. "The at-bats he was able to get were extremely crucial in his development. If he's ready to be a Major League first baseman, he can do the job. If he doesn't and has to go back to Triple-A for a short time or whatever, it will be a situation where he knows exactly what it's going to take for him to be a solid Major League player."
Mills is about a month removed from reconstructive knee surgery and was moving gingerly about the lobby at the Dolphin Resort. Mills spent part of Monday in a meeting with general manager Ed Wade and his staff, talking about not only the first-base situation, but also what moves the team might be willing to make.
"We're going to be as active as we can be trying to improve our club," he said. "If you go around our ballclub, we've got some pretty good players already in place [based on] how they played for most of last [season]. We can see that. We want to get better, but at the same time we don't want to tear down what go us better. It's going to be interesting to see what pieces are out there and how we can get better."
Mills believes the Astros have already gotten better offensively with the addition of Clint Barmes, who was acquired last month in a trade with the Rockies. He's penciled in to play shortstop, but Mills doesn't want to pigeon-hole him so early in the offseason.
"He's such a valuable player, such a good player and a guy we want on the field," Mills said. "If he fits there, that's where he's going to be. If he and [Jeff] Keppinger or whatever are going to do some things at second base, we'll see. There's no doubt he's got some value with us, and hopefully he'll fit in. There's no reason to think he won't, whether it's at shortstop or whatever."
Mills said he'd be open to Brian Bogusevic splitting time in left field, presumably with Jason Michaels, to start 2011, and he's anxious to see what top prospect Jordan Lyles can do while battling for a spot in the rotation.
"I haven't really had an opportunity to see much of him, but I've read all the reports and listened to what a lot of people have said, and they think there's no doubt he has an opportunity to fit into that mix we're going to have in that fifth-starter position," Mills said. "At the same time, I don't want to anoint him as our fifth starter. The guy hasn't had a chance to do it against Major League competition, so we'll get an opportunity to see moving forward where he's at."
Mills, who was hired last October after six years as bench coach with the Red Sox, guided the Astros to a 76-86 finish last season, overcoming two early eight-game losing streaks that led to a 17-34 start. He's no longer the junior member of the managerial fraternity, having been supplanted by a handful of new managers for 2011.
With a contract extension under his belt, an ever-improving farm system and a strong finish to last season, Mills believes the Astros are on the right path for success.
"There's no doubt that's something to build on, but the thing is these guys were able to see they could have success," he said. "They could have fun and they could win."