This is exactly what you need if you don't want to add a second drive to your iMac. I would also leave a budget for any parts that you might damage on the first try.
WD Blue Desktop 1TB Hard Drive - 3.5 inch, 5400~7200RPM, SATA3 (6.0GB/s), 64MB ๐พ Cache, Ideal for PC, Mac, CCTV, NAS, DVR, Raid and SATA Applications, 1 Year Warranty
176 Review
๐พ Seagate Compute 2TB Internal Hard Drive HDD โ 3.5 Inch SATA for Desktop PC (ST2000DM01C)
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Seagate 1TB Mobile HDD SATA 6Gb/s 128MB Cache 2.5": Internal Bare Drive (ST1000LM035) - Reliable Storage Solution for Enhanced Performance
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Seagate Momentus 2 5 Inch Cache ST1000LM024
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Game console Microsoft Xbox One X 1000 GB HDD, black
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8TB Seagate Backup Plus Hub Desktop Hard Drive with Data Recovery Services
56 Review
18 TB External HDD Western Digital WD Elements Desktop, USB 3.0, black
95 Review
Shock-Resistant Transcend StoreJet 25M3 USB 3.1 Slim Portable Hard Drive with 500GB Capacity
99 Review