I found a few different resources for a replacement jack. It also seems that the headphone jack and the scroll wheel are one piece, so that will likely need to be replaced as well.
* [link|https://eoe.works/collections/apple-ipod-nano-2nd-generation-replacement-parts/products/new-click-wheel-headphone-jack-flex-for-apple-ipod-nano-2nd-generation-black|Elite Obsolete Electronics|new_window=true]
* [link|https://www.ebay.com/itm/324896797335|Ebay|new_window=true]
To answer the second half of your question, you could probably upgrade your [link|https://hackaday.com/2020/08/04/bringing-an-ipod-to-the-modern-nand-era/|iPod's storage] and [link|https://hackaday.com/2021/01/18/retrofitting-usb-c-to-an-ipod-nano/|retrofit a USB-C port onto your device]. However, doing so would require a significant amount of micro-soldering skills and knowledge of the device's firmware.