Be sure you really want or care about the differences between "luxury" and premium cruise lines when you factor your costs.

Hold any cruise line to the premium cruise line costs first, before you pay extra for "luxury" because for the life of me I can't figure out besides the label, what the difference is from my own experiences on the two different types. If you get "luxury" for the same price and similar amenities as a premium line, then you might want to make a reasoned decision to go one way or the other.

But on the other hand, even all things being equal you might find you like travelling with travellers, rather than status-conscious tourists.

One "luxury" line actually has smaller rooms than the premium line, so strict price comparisons may still not be apples to apples. All cabins have pretty much the same layouts, and the difference will be in the quality of the finishings which may or may not matter all that much in the grand scheme of things depending how much time you might spend in your cabin.

Or, even outside on the balcony - which can be very, very different on similar cruise lines. Some are shallow and exposed. Some are deep and spacious. Some are in direct view of outside elevators.

With all the minute variables, it is best to just stick to price and itinerary first. Then start nit-picking "luxury" vs. premium stuff. it gets a lot less substantial down at that level so the price and itinerary differences have to really be significant to chose "luxury" over premium classes for similarly sized ships. It is just a few days out of one's life after all. "Luxury" actually even matters less on the longer cruises, if it doesn't compete in price and itinerary.