Think about pack load. On the other hand, if you've already trimmed pack weight, you can splurge on more camp comfort. Pick a pad that's appropriate for your weather. You'll have a warmer, more comfortable, and more versatile arrangement than any single pad. Buy for your size.
Pads come in different lengths and widths.
Consider your sleeping style. Heavy sleepers may not need lots of cushy padding, while light sleepers will want as much comfort as possible. Plan with your partner. Coupling kits are also available. Try before you buy.