This is a dilemma some people face and they feel their only option is to buy a king or queen size mattress to get the extra length they need.
Nowadays, people are often turning to a relatively new mattress size…………… the Extra-Long (XL). These are the same length, 80”, as a queen or king size. Extra longs are available in double/full, single/twin and even ¾ sizes.
I hear people despair of never being able to find the proper sized bedding, but an online search shows that they are available. Maybe not in as many versions as traditional bed dressing, but there is some choice.
So consider this an option. We can always lengthen the rails to accommodate whatever length your mattress is.