You need the correct freehub for the hub, you can't upgrade this component on it's own, it need to fit with the rest of the parts to make the whole hub.
For the part number needed, you first need to ID the hub, what we don't know from the info supplied is what hub you have, is it a Shimano? (not just Shimano compatible?) If it is a Shimano hub, find the part number of the freehub via
Shimano the number of the hub is printed on the center of the hub, either directly or on a metallic sticker. If it is another brand, the chance of getting spares is limited, and complete wheel replacement would probably be a cheaper option.
Regardless, for this issue, have you tried a LBS, they will be able to assist you rather than Amazon, who can't ID anything or give advise.