I think the lighting looks great in these! It's nice and even, but yet not flat. There's good catchlights in the eyes and no harsh shadows. Usually the goal with a basic studio lighting setup is to mimic natural light so the images will look just like what you've got here. So would a lighting setup improve your photos? Probably not significantly since it seems like you've already got natural light nailed down.
Plus there can be quite a learning curve when starting out with strobes, so it's not like you can take them out of the box and all of a sudden have great photos. I say keep doing what you're doing!!