FWIW I tried cruiser bars on a bike much like this one and they were still too low. Unless you get some handlebars with a lot of rise, I don’t think just the stem is going to do it. You can get a wider seat and push it back too. But really, you are trying to make it into a different kind of bike that already exists.

Even a brand new mountain bike has more handlebar rise than this thanks to the larger size wheels and suspension fork. You could look at one of those, or a comfortable town bike that sits you up completely.