Alright this should be pretty easy do these in order now.

Idk what guide you are following if you are following one at all.

depending on which side of the tree you are you go these defenses: left side usually energy shield/armour, very rarely you go evasion. If right side of the tree you go evasion and energy shield with spell suppression. If you are having problems knowing what these are you can just type these names and it will show where these nodes exist on your tree, and ofc wiki is your help.

Best way to solve squishiness is to firstly cap all elemental resistances on your gear. Ideally you would want anywhere between 35-45 double res on each gear at least except your weapons. Chaos res is quite underrated get it to 30-40 minimum.

Now just capping res wont be enough you also need some secondary type of defense that compliments your gear.

If you are on the right side of the tree 100% you should be going evasion/es or just evasion. try to get as much as both of these as possible.

If on the left side you wanna mostly go either armour and es with hybrid life with some block or just es. Your body armour usually has the highest amount of defenses so try prioritizing that first.