Maybe a walker just prop him up or a bouncy chair with soft back with a bar in front with toys
There’s a new one out that a pediatric physical therapist actually recommends because it puts the babies body in the right position. Let me see......
My pediatrician strongly advises against stuff like this. He said it forces kids to sit and their bodies usually aren’t ready until 5 months. We bought one when my son was 5 months and he literally used it like 4 times and then I gave it away.
My daughter has one and she loves it