Balfour was an old man well past his policy making years. He signed the “Balfour declaration” as he was in cabinet officially as foreign secretary, but in truth was somthing of a figurehead. This was all intra-party political arrangements due to the need for a WWI coalition government.
All these decisions were most likely made by the small group that constituted the War Cabinet.
I don’t care about Balfour. I care about the art.
Up to a point, but Balfour’s own part was a lot more significant than you suggest. It was the editor of the Manchester Guardian, C P Scott, who had been running a long press campaign arguing for a Jewish state, who was the vital link in introducing Chaim Weizmann to Balfour, as he was a friend of both. Balfour thereafter took a strong personal interest, and made vital (indeed passionate) speeches in support of Weizmann at the 1919 Paris Peace Conference. It was the Balfour/Weizmann double act in Paris which persuaded the allies to accept the principle, and thereafter to give Britain the provisional Palestinian ‘mandate’ (despite a tussle with France, who wanted the whole Levant including Syria).