Welcome, very nice modifications to your TW125.
Yes, there are commercially available oil coolers:For Sale Oil Coolers These pick up oil supply from the oil filter housing. With fabrication skills one can make a similar oil pick-up and then use an aftermarket pit bike cooler. The Mr.Gizmo bike I have has two heat exchangers made from coils of copper tubing; one uses the above listed oil filter cover and the other takes pressurized oil from the output shaft's outer bearing housing. While currently dismounted I could dig the snow out from my barn and take a picture of the modified left side cover showing oil pick-up...just ask!
Someone else with a 125cc might recommend good carb tuning details. I would not expect dramatic improvements possible greater than stock performance though.