Overstock.com offers the Lucid 2" Foam Mattress Topper in various sizes, as listed below. Plus, take an extra 12% off when you click through this link, dropping starting prices to $35.19. Shipping adds $2.95, but orders over $50 bag free shipping. The sizes, with prices after discount:

• Twin for $35.19 (low by $7)
• Twin XL for $39.59 (low by $3)
• Full for $43.99 (low by $23)
• Full XL for $48.39 (low by $28)
• King for $61.59 (low by $14)
• California King for $61.59 (low by $9)

Of note, Linenspa offers it in queen for $70.20 via coupon code "HOLIDAYS". With free shipping, that's the lowest total price we could find by $9, although we saw it for $10 less two weeks ago.