I recommend checking out a brick-and-mortar retail store that has demonstrator models of the Bose QuietComfort 35 II and/or Sony WH-1000XM3 set up. Ideally, I would also recommend checking out the more affordable options from Sennheiser, Audio-Technica, AKG, JBL, et al. for sake of comparison. At first they'll probably be playing some silly demo tracks through them, but you can easily pair them to your phone via Bluetooth and listen to your own music. Beyond being able to make a brief, subjective assessment of the sound quality, it's entirely worthwhile just to see if you find them comfortable on your head, and to experience the control interface for yourself. If you're lucky, the store will be noisy and you can test out the noise cancelling capabilities.
Once you've experienced them for yourself - even in a store environment - you'll probably have a better understanding as to whether the more expensive models are worth the extra cash or not.
Personally: I was gifted the QuietComfort 35s just over a year ago, and I think it's a brilliant product. I understand that a lot of audio forum type people would scoff at the idea of buying a Bose product - understandable, when you look at the most of their current offerings - but these are an exception. I mostly use them on my commute to and from work, but also use them fairly frequently around my apartment and yard.
To my ears, they sound pretty great. There are probably other Bluetooth ANC headphones that sound better, and there are undoubtedly corded closed-back traditional passive headphones that sound better (in a controlled, quiet environment).
But the thing I've come to appreciate about them over the past year or so, is that even if there are other headphones on the market that are cheaper, or are better in one particular area, the QC35s are great simply because they're good at everything. The decisions that were made in the product design process were so well-balanced in terms of trade offs. There isn't anything about them I would change if it meant that there were sacrifices to make in terms of battery life, comfort, build quality, ergonomics, requiring a cord, etc.
The only real weakness imo is practically inherent to over-ear headphone designs. It gets very hot and humid during an Australian summer, and I'd rather wear IEMs during these months.
