While britain won’t satisfy your need for survival - you will die if the enemy notices you and has time to shoot you properly. Still, with some angling you can bounce some shots once you’re at the sherman.
However, what britain will give you instead is lolpen. I have faced kvs and panthers and tigers head-on in my firefly and won because that thing is a monster if you can hit weakspots. It will not one hit kill, oh no. It will slowly torture the enemy by first taking out the gunner, then destroying the cannon/breach and finally murdering the replacement gunner or driver crew.
Early/low BR britain is painful though, as you use solid shot and you lack the caliber to have enough spalling to properly rake your enemies. However, starting with Cromwell I, the fun begins. Currently my line-up is an achilles, a firefly, a sherman 2 and a cromwell (supported by CAP spit F Mk IX) and I seem to do fine even in uptiers despite the large BR gap between 4.7 firefly and 3.7 cromwell.
Brits are very good at penetration. Achilles/Avenger (souped up achilles) and firefly.
As a bonus, the torture that is early british grind means you get far more consistent wins than you do with germany or u.s, as I feel my teams work together much more than when I roll around in my pz4s and vk3002.
And as a bonus, it really forces you to learn where ammo racks, gunners and all that are. This makes playing other nations much easier.
For your current choices, italy in air WW2 tends to have very nice teams. Consistently, whenever I get italian air teammates my matches go swimmingly. They communicate, they work together, they cover your six and they climb to altitude. Italy, being bit of a joke of WW2, kinda avoids people going to it based on history channel myths.
Playing as germany out of your choices… the tanks are awesome, but are ill-suited for many of the maps as you got non-existent side armour, no stabilizer, bad reverse speed and horrible turret rotation - a terrible combo for corner peeking. Plus, you gotta contend with wehraboos who ignore all this and suicide into the enemy because the tiger should be immortal, right?
So! Stick with italy, or give minor nations like britain or france a try.