Any of the rebranded FlySky 9X-type receivers should work -- so long as they're the same version.
V1 has the main receiver and a satellite, v2 has a single receiver with a sleeved dipole antenna (red lump)
HK has the 8-channel and 6-channel V1 and V2 receivers (the 6-channel ones are branded HobbyKing, the 8-channel ones are branded Turnigy) but they're usually on backorder so if the stock levels are zero you'll be waiting an indeterminate length of time for shipment.
The standard Turnigy receiver is a bit bulky, but not very heavy. You can reduce both weight and bulk by removing the case and wrapping in heatshrink or similar. If you want a smaller and lighter RX, use the HobbyKing versions. Choose either V1 or V2 to suit your TX version:
While the smartypants programming board is not needed to upgrade the firmware, it does not require any soldering if you have a version 2 radio. There was a mess up on the version 1 radio main board, they put the programming pads on the wrong pins.
The programing board also has a EL backlight, which is very thin, so no modding is required to get it to fit. just lift the main board up, pop the backlight on the back of the LCD and place the main board back down. could not be easier.
The ER9x firmware is sooo much better, far more capable - not even in the same league. I cant recommend it enough. AND it lets you turn off the incessant beeping with every button press!
On a side note, its interesting to see that while the turnigy branded radio requires you to mod it to be able to use the trainer function, the flysky one does not. I can only put it down to the turnigy radio module not having an input impedance on the signal wire, grounding out the signal when you plug in a cable.
hey guys thanks for the replies..... im just a normal 14 year kid who like to fly thingsss.... so i cant really mod my Fly Sky TH9X transmitter.... And sorry i do not know how to check the version of my transmitter