When preparing for a commercial jet flight it'd be nice to know how warm my clothes should be so that I don't freeze after sitting for several hours in say +16 degrees Celsius (61 degrees Fahrenheit).
What's the typical temperature in the passenger cabin? Are there air drafts? How cold and how warm can it reasonably get?
It varies, and flight attendants will often alter it over the course of longer flights as well (for example, on overnight flights they often turn up the temperature by a degree or two). Often there are drafts from the air conditioning, although it's hard to predict exactly where unless you often sit in the same seat on the same plane.
The traditional and best advice is to dress in layers; wear light clothing with a jumper/sweater/pullover, and perhaps pack a blanket or warm jacket in your carry-on bag (although many/most long-haul flights will provide basic blankets for each seat). This way you can warm yourself up or cool yourself down as you need.
Don't overthink it, though. Temperatures typically only vary by a few degrees.
I've never been on a passenger plane that was anywhere close to being as low as 16 C. Almost all of the ones I've been on have been either normal room temperature (~22 C/72 F) or warmer. Particularly when sitting at the gate in a hot climate, the cabin can get quite warm (27 C/80 F or more.) Sometimes sitting close to exit doors can be cold from what I'm told, but I've never experienced that myself when sitting by one. Sitting near the boarding door while it's open on the ground in a cold climate would obviously be cold, though. I would recommend wearing long sleeves, though, not only due to the possibility of a cooler cabin, but also because you probably don't want your arms laying directly on an armrest where a bunch of other people's arms, hands, etc. have been lately (either in the airport or on the plane.) Another reason for the long sleeves is that, even if the plane itself is warm, the jetways (boarding bridges) can be quite cold in cold climates.
During flight, the temperature will depend on what the cabin crew sets it to, but I've never personally experienced it being cold (and I've been on at least a hundred passenger flights and am cold natured.) For whatever it's worth, Korean Air states that they keep their cabins in the 23-25 C range. They also have some other tips for what to expect on board in that link.
As far as drafts are concerned, this would only happen if the person beside you is using their A/C vent and it's aimed partially at you. Otherwise, no, there are generally no drafts, since it's a sealed, pressurized cabin (I'm assuming we're talking about normal, pressurized airliners here, not tiny unpressurized puddle jumpers.)
An important thing to note, as has been mentioned in a comment, is the low humidity in the cabin. This can dry out your skin, eyes, etc., especially on long flights. If you don't like for your hands to be dry, you might consider taking moisturizing hand lotion with you. However, please, for the sake of the other people on board, do not take scented hand lotion (or wear a significant amount of perfume, etc.) Remember that you are in a closed vessel with a lot of other people, many of whom are probably allergic to perfumes and most of whom probably don't want to smell it, even if they aren't allergic.
NORMALLY, temperatures in a cabin will be room temperature.
There are occasions when it will be a few degrees colder, either because of the outside air temperature, or because of the air-conditioning. In such instances, ONE extra layer of clothing will be helpful.
You can "carry on" that extra layer of clothing, but if you haven't, you can ask for a blanket or other covering from the flight staff.
I think temperature depends upon the type of aircraft and seat position. During BA June 2018 flight on an Airbus 320 from Munich to London, we had the old style twist vents above the seats that allowed for cooling during the warm flight.
That same day on a BA Boeing 787 from London to San Jose, CA, we no longer had the overhead twist vents, and being stuck in a middle seat was absolutely awful from an overheating standpoint.
