Your current setup (juice and system) is weaker (lower nicotine) than the Juul was. Percentage nicotine is 10 times mg/ml (i.e. 3% = 30 mg/ml), so you’ll have dropped from 30 mg/ml to 3 mg/ml. Part of that will be offset by the fact that the Nord is more powerful and will vapourize more juice per puff, but that’s probably not enough of a difference to make up for such a dramatic drop.
So, what you need is juice with a higher nic level and a different flavour. With the NordX, you won’t want as much nicotine as you had with the Juul, so you might want to try something in the range of 6 – 12 mg/ml. Before you go looking, I should mention that there are two types of nicotine, freebase nicotine and salt nicotine. The Juul used salt nicotine, which has less throat hit (that catch in the back of your throat when you smoke or vape) than freebase. Your current juice probably has freebase. Salt nic was developed so that people could use higher concentrations of nicotine without choking on it. Which type you prefer is up to you, but with the Nord X you might want to try freebase if you’re using 6 mg/ml, but consider salts if you go up to 9 or higher. Actually, if you’re having throat irritation you might want to go straight to salt nic (and lower your wattage a bit.) In case you end up wondering which kind of nicotine a particular juice has, juices using nic salt will usually say so. If it doesn’t say it’s nic salt, you can generally assume it’s freebase.
As far as the flavour goes, it’s really a matter of trial and error to find something that you like. I’d suggest buying a few small bottles with different flavours and nicotine concentrations until you find out what works for you. One of the base ingredients of ejuice (vegetable glycerin) is a bit sweet so you’ll never find a juice that isn’t a little sweet, but most manufacturers also add varying levels of sweetener to their flavours. You’ll just need to try a few options ’til you come up with some flavours on the lower end. DIY (making your own juice) is also an option, but you probably don’t want to go there at this point.
Finally, concerning the overall approach to freeing yourself from the nicotine beast: You’re off to a good start. Juul and some other pods can be a bit problematic for some people because their nicotine levels are so high, so you’re better off using a different device – especially one that lets you use juices with different nicotine levels. That said, my advice is not to worry too much about the nicotine at first. Most of the harm from cigarettes comes from the smoke, ash, tar and carbon monoxide you inhale, not the nicotine, so the priority is to get rid of those. Additionally, many people (although not everyone) find it much easier to cut their nicotine after they become adjusted to vaping than it ever was to cut down on cigarettes. My recommendation, whatever it may be worth, is to do what you need to do to make sure you stick to vaping and avoid cigarettes. If you start craving cigarettes, increase your vaping or your nicotine level. Once you become comfortable vaping and no longer crave cigarettes, then it’s time to look at reducing your nicotine levels (at whatever pace works for you – the key is not to push it so hard that you relapse to cigarettes).