Yes, that is the correct approach. You are accurate that selling personal-use items (whether clothing, furniture, or household goods, etc.) in a transaction that results in a loss (less than the original purchase price) means the loss cannot be deducted, but it would not count as taxable income either! A 1099-K issued to you should be reported with a cost basis equal to the sales price, so that the gain/loss nets to zero. This is the correct approach to demonstrate to the IRS that you have not omitted any income.
When you amend your return, just add the 1099-K to the records you will submit and provide documentation indicating this was a personal item sold at a loss (receipts or photographs or notes are a reasonable documentation of personal items). IRS just wants to see that your amended return now matches the 1099-K sent to them, so this is reducing audit flags, rather than increasing them.
If you never intended to run a resale business, this is also fine to do if it is clear they are personal items. Just keep copies of your amendment and supporting documentation if the IRS ever wanted clarity.
(Optional helpful reference: IRS Topic No. 409 – Capital Gains and Losses)
