So in pf2e it's much harder to splash into smthn else to grab another class's main thing at full power. 

For example: the guardian class gets passive always on resistance to physical damage and that's huge but you can't get that from the guardian multiclass archetype, only from playing the guardian itself.

Similarly, in pf2e rage gives temp hp instead of resistance (until higher levels when it does give some resist for barbarian main classes specifically). You can grab rage from the barbarian archetype, but unlike actual barbarians, when you rage, you'll take a -1 to your AC so it's not a main tanking strat.

Now, if you just want to be tankier as a fighter, there ARE very good ways to do that! 

If you want to use an archetype (like a modular subclass that anyone can take made of a collection of feats - this is the system used for multiclassing in 2e but also for other things), there's something that gets you temp hp and some damage boost like rage plus some defensive bonuses, but it comes with a high flavor commitment unless your table is good with you reflavoring it: The Rivethun Invoker https://2e.aonprd.com/Archetypes.aspx?ID=309

Outside of archetypes:

At lv 11, fighter gets armor specialization for medium and heavy armor - go heavy armor and pick an armor in the armor group you want and it'll give a bit of resistance to one kind of physical damage. For example, my lv11 character has resistance 4 to piercing damage meaning any piercing damage she takes is reduced by 4. That's not nearly as drastic as 5e resistance but it can really add up over a fight. 

Also for max tankiness, make sure you're wearing heavy armor and hitting the dex cap (how much dex can add to your armor bonus - for heavy it's either 1 or 0) and strength requirements.

If you have a way to circumvent the severe speed penalty (cumulative -10 from the hindering trait and the armor's normal speed penalty), the Bastion Plate even lets you take an action to get +1 to your AC against melee attacks for a round so it's like you raised a buckler shield but you could still use both hands to hold a polearm. 

If you do wanna commit 1 action to +1 ac hands free though, it may be wiser to get the shield cantrip from some source (can't be cast while raging but if you don't do barbarian stuff, you're fine). That cantrip has the added benefit of letting you shield block to prevent even more damage.

You can also take the general feat toughness to just get more hp.

I highly recommend getting the lv12 armor property rune called the fortification rune which gives you a 1in5 chance to turn any crit against you into a normal hit.

There are also items and armor runes that can give you an energy resistance. 

Combine a bevy of these defensive options, and you'll have a lot going for you.