[DonRotolo]

It would be helpful to know the precision requirements you are thinking of.
I am not aware of any off-the-shelf gizmo that does what you want; there probably is such a thing, you need to spend a few hours on Google.

The easiest thing to track would be a light source. Radio is directional, but not nearly as directional in such a small space as light. Also, tracking RF precisely is much more difficult than tracking a light source.

There are linear CCD sensors available - think of a camera that has only one row of pixels. An inexpensive one might have 128 pixels (1 x 128), so you can detect 1/128 of the field of view (which needs to be managed with lenses). Using two such sensors, you can triangulate (in real time) the location where the lines intersect - but at low precision at larger distances. The solution to that would be to use multiple sensors, perhaps six (one at each end plus two on eqach side - but this might have a blind spot in each corner) or even a few dozen.

The player would wear a belt (a necklace seems dangerous to me) with a small battery pack and a few LEDs of a certain color - other colors need to be filtered out of the sensor's incoming light. (IR is probably the easiest).

Pick the sensors that report the highest brightness every (pick a time period, maybe 50 milliseconds), use a lookup table to determine the abcolute location based on the pixel value reporting highest brightness, and you have your X,Y player location.

Write back if you want to get into details, including devices.

Don