To protect yourself, yes. For non-cash donations of items, where the value of a single item or "group of similar items" is more than $5000, you must have a signed appraisal by a qualified appraiser, the appraiser must sign form 8283 listing the donation, a financially responsible official of the charity must also sign the form 8283 acknowledging the donation, and you must mail the original signed form 8283 to the IRS after e-filing your tax return. (You can place the information from the 8283 in electronic form in Turbotax so your e-filed return will contain the donation, but then you also have to physically mail the original document.)
There is no clear rule on what "a group of similar items" means. Potentially, if you divided the donation into "Furniture", "Toys" and "Clothing" and each group was less than $5000, that might get past an auditor and save the price of the appraisal. But I'm not sure it's worth the risk. If audited, your deduction might be cut down to $4999 or less.
If you don't get an appraisal, you will definitely need your own records to determine the value, this should be a detailed inventory describing the item, condition, approximately when you acquired them and the price you paid, and the present fair market value. You will also want a receipt from the charity that acknowledges the donation, and I don't just mean a blank template form that a place like Goodwill might give out. There have been cases where the IRS has said "I see your list of items and your pro forma standard receipt, but can you prove you donated the exact items on this list to the charity on that date?" You might have someone from the charity sign your inventory to acknowledge receiving those specific items.
Review IRS publication 526 for the details.
https://www.irs.gov/pub/irs-pdf/p526.pdf
Or, hire someone to sell the items at an estate sale and then donate the cash.
