From TV ads of the 60s: Double your pleasure / Double your fun / Chew double-good, double-good Double-Mint Gum. Of course, 'increase' would be less exact in measure, but 'double' seems to be the standard. For example, "double your trouble" isn't taken literally in most cases, but the phrase does the job.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.