While the Mets explore options for addressing their primary remaining need - setup men in the bullpen - they are investigating choices at second base, too, and they are one of three teams interested in former All-Star Bret Boone, according to a baseball source. The Rangers and Padres are also involved, and it's likely that Boone will sign a minor-league deal with one of the three clubs and get an invitation to spring training, the source said. If Boone signs with the Mets, he could push Kaz Matsui at second, or perhaps take over the position if Matsui is unloaded via trade, which the Mets hope to accomplish. Of course, that's assuming Boone can right his career, which took a sharp downturn last season when he was released by the Mariners and Twins and hit just .221 with seven homers and 37 RBI in 88 games, 74 with Seattle. Minnesota dumped him after only three weeks.