I'll second the Tortuga recommendations; I've had a Tortuga travel backpack for close to 6 years now, and have not used "conventional luggage" since then. I can generally get about 7-8 days worth of stuff in my bag, which looks
something like this (not the exact model but close). If it's at trip longer than that, I plan on doing laundry at some point. Did a 16-day trip to South America with this last summer and only had to do laundry once at an Airbnb.
The only items I won't re-wear are underwear and socks. Plan for <the number of days of your trip> + 1 backup pair of each. For pants, plan on 2 days of wear each, maybe 2.5-3 if you really want to stretch it and you're not, like, a slob. Try to pack lighter top options. Going somewhere cold? Maybe some light sweaters or long-sleeve dress shirts rather than bulky sweaters. Need to wear a heavier coat? Wear it on the plane and don't pack it. Every item of clothing, clean or dirty, gets rolled up as compact as possible. Bring a garbage bag for the dirty clothes to separate them from the clean stuff, but roll them up too in order to save space. Actually plan what you're going to wear, and be aware that you're not gonna have a myriad of options on any given day....you're gonna wear pretty much everything you bring, so choose wisely. Check the weather where you're going.
Only take the bare essentials of everything else. Phone chargers, voltage converters, headphones, etc., get as small as possible and pack in ziploc sandwich bags. Toiletries, only the max allowed of soap/shampoo, toothpaste, toothbrush, deodorant, razor, nothing non-essential. Usually take 1 book and I'll buy a newspaper at the airport if needed.
I think the only way this wouldn't work is if you're going to a really cold place and need a ton of extra layer gear, I think.