Put some gravel from the 38g in the 10g. There isn't much bacteria in the water. They like to stick to stuff, so gravel, ornaments, and plants have more.....plus the filter media. You could move some water just to keep the same pH and temp for him.
You need something to keep the water moving....stagnant water is not good. An air pump would be fine, but I'd use a valve to keep the bubbles down. If you can get a sponge filter, that would be ideal. They have some surface agitation when used with an airstone, but nothing like a HOB filter. Otherwise, I'd just go ahead and get a small HOB, like the Red-Sea nano filter.
As for stocking...I'd skip the Cories. Really the only ones that should live in a 10g are the Dwarf Cories, and even they need more swimming room. Also, they like large groups to feel secure, so having 4-5 of them wouldn't be good. Instead, you could get a school of Harlequin rasboras. They are Betta friendly and colorful.
Don't overfeed and do weekly water changes and gravel vacs and there is no need for a bottom feeder fish.
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