The size of a TV is inversely proportional to its WAF or Wife Acceptance Factor.
One way to trick your wife into allowing for a larger TV is to replace all the other objects in the room with ones 20% larger so the TV suddenly appears too small, its like the opposite of trimming your bush.
Seriously though here's some tips on how you get a new and/or larger TV when the old one is still working fine:
1. Suggest putting it on the wall to "save space" in the room, when it goes on the wall it will look much smaller and it might stick off the wall cause its thick, now you "need" a new TV to "keep the aesthetics of the room in balance"
2. Take the fuse out of the plug: "the power supply's failed love, I've read about this online"
3. Leave a looped video of objects being thrown around at high speed on the TV for your child to watch then "accidentally" leave a box of bouncy balls sitting next to the child.
4. PM a friend who recently got a new TV and have them encourage their wife to make a social post about it that your wife will see: "The media wall turned out so great let's flaunt it darlin!"
5. Watch Game of Thrones or House of the Dragon and make sure you have a subscription for 4K HDR on the streaming service: "I cant see a bloody thing going on love, battle of the blind bastards more like!"