You could consider B.t. 'Golden Ruby', a newer dwarf cultivar with orangey-red foliage with a bright yellow-green edge. And I really like 'Orange Rocket' which is like a copper colored scaled down version of 'Hellmond's Pillar'. But that may be too tall for your needs.

Is not Japanese barberry considered an invasive plant in Wisconsin?

I just came across those and they look promising. Pygmy Ruby looks good to. Rosy Rocket is another nice one for a width restrictions.

I'm shooting from the cuff right now but I believe the species plant is listed as an invasive due to vigor and thorns.

The smaller cultivars for a landscape situation are no problem.

I doubt you will find the restrictions limited to just the species. To my knowledge there are currently no sterile forms of Berberis thunbergii, although a great deal of research is being conducted into their development. The plant is considered invasive because it grows easily and freely from both seeds and creeping roots/rooted stems. Birds and rabbits eat the seeds and disperse them over a wide area. Cultivated forms are just as likely to flower and fruit as is the straight species and therefore can be spread and dispersed just as well.

FYI, thorns have nothing to do with invasiveness :-)

Orange Rocket has phenomenal color but it is newish and I am not sure how well it holds its color in heat and sun; I bought a few last year and if they hold their color well I'll get some more. Admiration is another nice one with yellow margins that I am also testing out for summer color. Per Plant Haven (holds the patent) they have not yet observed flowers on Orange Rocket. We have a number of evergreen Berberis here with red/maroon leaves but I don't think that any are hardy in your zone.

GG, not sure on that one. I've actually never seen them outside the home landscape. They've always behave in the space I've allotted for them. I don't mean to sound naive but I really don't hear the local gardening community talking about their invasivness.

I remember seeing awesome color on Orange Rocket but they garden centers sold out pretty quick!

More than one existing selection already in production is claimed to be not producing numbers of fruits. See the web sites of big name wholesale nurseries that continue to introduce cultivars of Japanese barberry.

Independent outlets here present spreads of multiple different ones each year. If it were me I'd go look at what they have, see if the look I wanted was being presented by a particular kind in stock at the time.

Last year I found one that interested me, based on the depiction given by the introducer on its web site - only to see it having been recently delivered to the retailer (by the originating company) infested witha leaf spot problem.