I can't comment about the Widex Unique 440 because I don't wear them but I can comment about the Oticon Opn1 which you said you're going to try them out as well.
If you have an iPhone, you can pair the OPN1 with your iPhone and it'll give you a choice to independently set the left and right volume separately, so this feature may help you adjust to remove the imbalance. Once you know where the left and right volume settings should be relative to each other to minimize the imbalance, you can have your audi program the relative left/right volumes into the OPN directly so you won't have to keep making adjustment on the iPhone anymore. If you have Android phones then the Android ON app from Oticon doesn't have separate left/righ volume controls, unfortunately.
In terms of the background noise being way too loud for you, it's probably because you're not used to hearing better with the Widex Dream before so now everything will seem too loud for you. Just give it time to adjust and eventually your brain hearing will learn to become not as sensitive to the background noise as before. In the meantime, the volume control is your friend to turn things down if you feel too overwhelmed, and turn things back up when you need to listen to speech. The OPN has a built-in feature to gradually adjust your volume after so many hours if you want to set it, but manually adjusting the volume gives you more flexibility although less automated and a little more hassle.
When you try out the OPN, you'll probably also hear a lot of sounds around you that you did't hear before or don't care to hear now either because you consider those sounds noise. But keep in mind that the OPN1 lets you hear everything on purpose because that's an integral part of their "open" paradigm. But you'll also find good clarity in speech amongst all the sounds. So you need to give it time for your brain hearing to get adjusted to the new hearing capabilities and eventually your brain hearing will learn what to ignore and what to focus on quite seamlessly. With you still being young at 27 I'm sure your brain hearing will adapt quite well and quite quickly to the "open" paradigm. After a while, you'll be glad that you can hear everything and have your brain hearing be able to pick and choose what you want to focus on hearing and what you want to ignore at will. That's how normal hearing people selectively manage their hearing anyway. I wear the OPN1 and when I'm in a noisy moving car with the radio on, I notice the radio music the most, but if I want to shift my attention to focus on the other sounds beside the radio music, I can immediately notice the other sounds at will as well like they're right there at the tip of my fingers.
HA wearer since the 1990's > Rexton Insite+ CIC (2011-2016) > Oticon OPN RITE (2016)
KHz 0.25...0.5...0.75...1.0...1.5...2.0...3.0...4.0... 6.0...8.0
Left ...10...10....10.....30.....70....75....80....95.. ..90....80
Right .25...30....40.....55.....75....85....90....90...1 00...100