I asked a similar question for my four month old a few months ago, and got much more supportive answers, sorry everyone’s jumping on you, OP. The recommendation that I got, and loved, was the Fisher Price Sit-Me-Up Chair. Much better for them then the Bumbo, it actually helps them practice balancing in a sitting position.
https://www.amazon.com/Fisher-Price-GGD48-Sit-Me-Up-Floor-Seat/dp/B071ZBB11K?th=1
Obviously, not something you want them in for hours a day or anything, but great when you need 10 mins to unload the dishwasher. We used it for 5-15 mins probably 2-3 times a day until our little guy could sit independently. Very helpful!
Then once he was good but not perfect at sitting, we just put the boppy around him to break his occasional falls. But that sit-me up chair was great to bridge the gap. Especially because as he was getting close to sitting he wanted to sit up ALL THE TIME and we just couldn’t help him endlessly.