There is an aviator harness for budgies and lovebirds, I think it is the mini size
@Parrot Hotel & Shop has them.
Congrats on the harness training! You should tell Grumbles the harness won't eat him
Jack honestly thought the harness was going to eat him too and scream in retreat. Big boy really doesn't fear much, but a simple string---TERROR! haha
I initially just left the harness out in the open so he could see it even from his cage(about a week). Eventually, I worked him up to 10 min sessions of sitting with him and holding the harness in one hand and giving him a treat whenever he touched it and making sure I always ended on a good experience. Then I'd make the biggest loop possible and he'd have to stick his head through it to get the treat I was holding on the other side. I stayed at this step for weeks because he'd get very skittish and wouldn't consistently approach. He'd try to find a way around the loop to get to the treat. haha I'd also take the harness and drape it over my arm or around my neck, making a big deal over how fun this was while he watched me(as silly as I felt, I know he clued in on the "Oh, she's not dead!"). And then yesterday I sort of went for it and got the head loop over him, immediate treat and took it off. And since he didn't react much, I kept progressing in that same 10 min window. He gets the occasional treat with praise, but I also vary it with just lots of praise, scritches, and now the new reward will be trips outside. The head loop was the biggest NO-reaction. Once that's over, he settles right down and lets me loop his wings in(with a little growling while he figures out what I'm up to, but nothing that means business, just "I'm not sure what you're doing, but okay"). Tightening up the harness was a little trickier because he starts to fidget and I wanted to move fast so he didn't tangle himself, so that took more practice on my part than his, but 2 tries and I feel comfortable with the process. These were all things I read online or saw in various harness videos and then I tailored to Jack based on how I read his comfort and what he reacted well to the most.