I can talk to you about the jumper, since I've never used an exercauser. According to my pediatrician and my son's physical therapist, the jumper is not a good idea until your son has been crawling for at least a month (or so). It's very important for your son's development that he crawl. (There is a lot of research you can find on this, and differing opinions. But not crawling is linked to later learning abilities, specifically in reading and writing, and things such as difficulties learning to ride a bike.) The issue with the jumper, or a walker, or having baby stand and walk with mom and dad's help everywhere and often, is that they develop their standing muscles before their crawling muscles. Because the standing/walking muscles are bigger, they activate those when learning to crawl and often either don't crawl, or do it "incorrectly". Specficially, the cross-crawl is important for development.
I learned so much in physical therapy. We had an excellent pediatric therapist and I trust her completely. She knows her stuff. We had to make great effort not to stand Rowan up on our laps all the time and help him walk before his time. It's very natural for parents, grandparents, etc. to push for the walking. But really, we should push for the crawling and once that's well underway, walking will come and we can help! You won't miss out on anything, you'll just put it off for a while! Once my son was crawling, we put him in the jumper and he loved it. Also, FYI, we had a walker and as long as my son couldn't touch the ground and push up (which would develop those standing muscles) we could put him in it and he loved just sitting in it, and playing with the toys. Another great tool for sitting is the bumpo seat (which you're using). It helps them to develop their sitting muscles and head control.
In regards to activities, it sounds like you are doing great things! Tummy time for sure. Be assured your son is learning so much from you! The only suggestion I could give would be...do you have a baby carrier? Your son will learn a ton from going around with you while you work in the kitchen, or switch the laundry, etc. Also, baby/mom groups a couple times a week can really break the day up. I was also recently given a great suggestion to use grocery outings as a chance for an activity with my son. Rather than feeling pressured to shop, I can use the store as a way to teach him about foods, etc. Let him touch, feel, etc.
Your baby will be up and moving in no time and then things get really interesting! Enjoy this non-mobile time now! ;)