I would definitely not keep anything together with puffers, and that means cories too. Cories does not seem to learn from their mistakes, so they wouldn't be smart enough to stay away from a puffer, even if the puffer has nipped its fins several times. So no cories with puffers!
I have no experience with goldfish - all I know is that they like cold water, so you need a cory species that also like low temperatures. That excludes c. sterbai and c-121 among others, as they like warm water (they are one of the few cories you can keep with discus). Brochis multiradiatus is a cold water cory, but is very, very sensitive to the water quality (more than puffers), so they are hard to keep. They also need plenty of room.
I took a quick search of other cories that wants cold water, and these came up:
Corydoras adolfoi (i:12, k:99) 60mm (2.4") 20.0-26.0°C (68-78.8°F) 5.6-7.0 36733
Corydoras bondi (i:9, k:6) 50mm (2") 20.0-24.0°C (68-75.2°F) No data 6649
Corydoras brevirostris (i:12, k:19) 60mm (2.4") 20.0-24.0°C (68-75.2°F) 6.0-7.8 11041
Corydoras condiscipulus (i:8, k:10) 65mm (2.6") 20.0-25.0°C (68-77°F) No data 5933
Corydoras davidsandsi (i:12, k:25) 60mm (2.4") 20.0-25.0°C (68-77°F) 6.2-7.2 11553
Corydoras duplicareus (i:12, k:54) 55mm (2.2") 20.0-24.0°C (68-75.2°F) 6.4-7.4 18639
Corydoras ellisae (i:2, k:3) 65mm (2.6") 20.0-26.0°C (68-78.8°F) No data 3865
Corydoras leopardus (i:11, k:12) 75mm (3") 20.0-25.0°C (68-77°F) No data 9845
Corydoras orphnopterus (i:4, k:3) 70mm (2.8") 20.0-24.0°C (68-75.2°F) No data 4327
Corydoras paleatus (i:20, k:266) 70mm (2.8") 15.0-25.0°C (59-77°F) 6.0-7.5 46880
Corydoras polystictus (i:5, k:6) 50mm (2") 20.0-25.0°C (68-77°F) 6.0-7.6 5093
Corydoras simulatus (i:16, k:13) 70mm (2.8") 20.0-25.0°C (68-77°F) 6.2-6.4 11540
Corydoras treitlii (i:4, k:1) 70mm (2.8") 20.0-25.0°C (68-77°F) No data 3622
Corydoras trilineatus (i:20, k:151) 55mm (2.2") 16.0-25.0°C (60.8-77°F) 5.8-7.2 42123
Corydoras venezuelanus (i:24, k:42) 55mm (2.2") 19.0-25.0°C (66.2-77°F) 6.8-7.8 15558
Corydoras zygatus (i:8, k:19) 70mm (2.8") 16.0-25.0°C (60.8-77°F) No data 8348
Some of those needs a pretty low PH though (i.e. c. duplicareus).
Corydoras trilineatus is a nice cory. Easy to keep and easy to get. Look for cories sold as c. julii - they are always c. trilineatus. Actually I've never seen a real
c. julii in any shop, they've always been c. trilineatus. The difference between them is that c. julii have perfectly round spots, where c. trilineatus often have a more brain like pattern. But trilineatus can have more round spots as well. If it's a julii, it have to be wild caught. There are no juliis bred in captivity.
But whatever cory you choose: they need to be kept on sand. Gravel excludes keeping cories.