If I want to place two twinxl mattresses side by side to make a king size is there any way to match the heights if they are different thicknesses?

Yes, you can match the heights of two Twin XL mattresses placed side by side to make a King by using a few practical methods. Some are better than others. Here’s how:

Mattress Toppers or Pads

Add a topper to the thinner mattress to even it out. Choose a dense foam topper (but not memory foam) of the right thickness. Example: If one mattress is 2 inches shorter, use a 2 inch topper.

Adjustable Bed Base (one of the best ideas)

Some adjustable bases let you independently raise/lower each side or the they have adjustable height legs—ideal for mismatched heights.

Custom Cut Foam Layer

Buy a custom-cut foam piece (from upholstery or foam shops) to match the difference exactly and place it under or over the thinner mattress.

Custom Height Box Spring/Foundations (one of the best ideas)

Some companies (like Nine Clouds Beds) will let you order custom height foundations to closely match the two total heights of you twin xl mattresses.