Okay, my advice for what it is worth (because I am a non-conformist on the RS forum)
Condor states (and this is pretty typical of the European Carriers:
All passengers in Economy Class may carry one small personal item and
1 bag measuring up to 21.6 x 15.7 x 7,8 in (55 x 40 x 20 cm) and
weighting up to 13 lb (6 kg).
The weight of the cabin bag in Premium Economy Class must 18 lb (8kg).
Customers in Business Class are allowed to take 2 bags into the cabin
with a total weight of max 26 lb (12 kg).
So, for me that would mean a 21" Hard Side Spinner. For me just easier to deal with. The lightest one you can find. Mine weighs in at just a hair under 6.5 lbs which means I can pack about 11 pounds of clothes. Well, the volume of that bag wouldnt hold more clothes than that so it works for me. But clothes only, because they allow a personal item with no weight limit.
Condor doesnt state the size of the personal item, but has to fit under the seat (if required by the flight attendant). Turkish Air sets that at 40 x 30 x 15cm (15.7 x 11.8 x 5.9in) and thats a pretty good guide. The beauty is no weight limit. So pack it with all the heavy stuff. Fabric only in the carry on and everything else imaginable in the personal item.
Okay, that's the limitation. Is it enough for 3 months? Do you only do laundry at home once ever 3 months? Some people carry a weeks worth, others two weeks, both possible within the limits for most of us. Then before you leave locate where you will do laundry along the way. Sure, I guess I could do the 1 gallon zip lock shake and wash routine, but I am spoiled and rely on hotel laundry and nearby laundry services; I am on vacation after all.
Why the hardside spinner? Well, this is being debated on another thread, I just find it all around easier to deal with and if you buy the right personal item you sling it over the carry on handle and you are carrying zero weight on your body. But its a personal choice.
In short, yes, you can do it. I would at least give it a try before I start messing with checking or multiple bags. Nothing worse than dealing with a carry on AND a checked bag (then you really do need a spinner cause its miserable to drag two bags behind you).
If you are interested in my gear, PM and I can send the names, but I dont carry designer or name brand stuff. Its all pretty cheap and has lasted for years and years and years.