I would suggest getting the biggest size possible since spending more for TV is now only worth if you are going to be watching HDR content. All the other features are mostly just gimmicks.
What's your viewing distance? 43 is alright if you'll be sitting 4-6 feet away. Any longer and it's better to get a 49" or a 55" TV. Remember, you can change almost everything about the TV(smart - Chromecast, firecast. Audio - soundbar etc.) except the size and panel quality
Xiaomi has recently launched 75 inch 4K TV. See whether it will fit your budget or not. As mentioned above, the size of the TV depends a lot on the size of the room and viewing distance.
