Some teams prefer to estimate effort in a relative way using T-Shirt sizes.
For example, the “s” card represents a story that requires a relatively small amount of effort to complete. The “xxl” card represents a story that requires quite a bit larger amount of effort to complete.
Try this: Before backlog refinement and prioritization, have the team estimate the upcoming stories using the T-Shirt size deck. This will help the Product Owner understand how much relative effort is required per story, and s/he may be able to make informed decisions based off the relative T-Shirt sizes given.