First, the bad news. The vast majority of indoor TV antennas suck. Just about everyone has gone to that horrible "flat" style popularized by Mohu, with little multipath rejection. Who cares if it works - the important thing is that it's flat!
Sometimes I think the DVR+ itself was influenced by the "flatness" craze. Luckily it matters much less for electronics than antennas; the DVR+ of course works fine.
And their claims are grossly exaggerated, often claiming 100+ miles, which is impossible unless you own your own TV tower, or "4K," which will be true someday, but not now, and not with the DVR+, and has nothing to do with the antenna itself anyhow.
What you really need is an antenna with a reflector - which means it can't be flat since the reflector will sit 5" or so behind the antenna itself - and as wide as you can find. I wish Winegard still made the SS-3000, although it was amplified and I generally avoid amplified antennas. (Even if your signals are weak, an amp won't help much, but if you want to try one, buy a separate Winegard "Boost" LNA-100 vs. an amplified antenna.) Terk's HDTVi was good too, but it's no longer made either; after all, it wasn't flat!
That said, the Winegard FreeVision is a reasonable choice, even though technically it isn't an indoor antenna! Luckily it's small enough to mount to a stand and put on top of something. I have one on top of my fridge. It's not super, but at least it has a reflector, which gives it some UHF multipath rejection from the rear, and some ability to receive VHF-Hi (RF 7-13) signals as well as UHF (RF 14+) ones. Here's an Amazon.com link for the FreeVision: https://www.amazon.com/Winegard-Free.../dp/B003L76BJS
GE and RCA also make some OK antennas that can be used indoors, although they also sell some crap. For the good ones, you'll again have to rig up a stand.