you have a rather big selection of ff games on the psp.
if you want easy, 7-9 are all mostly good, though 8 has a potentially complicated stat mechanic thats less user-friendly than 7 and 9.
1 isn't exactly hard, but its annoying in many regards, especially with random encounters (at times, you might battle something on every single step.)
2 is the furthest thing from beginner-friendly with its unintuitive character-development system and I would not recommend it to anyone.
3 you have already played. its ok. the remakes are all supposedly made to ease people into the game.
4 + after years... well, the main game of final fantasy 4 is easy for the longest part. things can get slightly annoying towards the very end. but its very doable. as for the after years, while the chapters of all the characters were mostly enjoyable, if not very repetitive after a while, the whole thing ends with an annoyingly long super-dungeon filled with countless boss battles and barely enough story to fill a napkin. its beyond frustrating since you have a giant selection of characters, most of which are really useless and half of which will be crazy underleveled by the final story chapter, forcing you to grind and grind and grind.... play the main game is what I'm trying to say here, ignore the after years.
5 can be played on gpsp kai emulator, though it'll run laggy at times, making frameskip a must. even then, the music will be crackling every once in a while, slowdown will happen when theres weather effects. its playable though. its not as easy as 4, but it has a class system that is comparable to that of 3 which can be enjoyable and makes the game very easy if you know what you're doing. might also make it really hard if you dont.
6 also on gpsp kai, same issues. it might even run a bit more clunky than 5. but its still playable too. there's the option to go for the ps1 version (which is the snes version basically) but that has ridiculous loading times for battles and battle animations. 6 starts off easy and gets harder as it goes along. personally, I've only bothered to finish the final dungeon once, since it forces you to use all your characters in split parties, even though half of them will suck and for a firsttimer, its easy to lose one character forever and never even find 3 of the others.
it does have one of the most enjoyable stories though.
7 graphics are terrible by todays standards, they really didnt age well, but its easy. by god, it might be the easiest there is, hidden bosses taken aside and all.
8 graphics are a bit better, but not too much. many people don't like the characters in this one a lot. can be easy if you're willing to spend some time playing the card-mini game to get lots of helpful items easy and early.
9 this is basically a back to the roots for the series, simplifying a lot again. its pretty easy, has lots of things for you to do and it looks rather nice, even today (since they went with a more cartoony world style). the characters are also more likable than 7 and 8s. you can basically finish the game with characters on level 5 or so, so that says a lot about how easy it can get once you know a few tricks. it does require a lot of micro managing with support abilities and worn items to be easy though. you'll also spend stupid ammounts of times, stealing items from bosses.
then, theres dissidia, which is a final fantasy themed 3d beat em up. some love it, some hate it. it certainly has frustrating moments.
if you wanna give it a try, just go for 012 duodecim. it basically includes the original game and has more characters and story
crisis core is probably uninteresting to people who dont care about ff7, but it is also easy (if you dont aim to finish all missions and such) it also has difficulty options if you look for a really easy game. it does look good too. very good.
type-0... i'd say its too complicated to be easy. looks cool, but the cramped controls (lots of R+some button to dash, to avoid, to block, L+other buttons, to do this attack, that attack, reflect, L+R+ button to summon something, use special magic, items blabla combination stuff... too cramped up for me) really hurt the game.
characters in this are also plentiful and they all kinda suck. which is terrible, considering the world they build up in this game is very interesting...
final fantasy tactics - never got into it. battles took forever, you always miss your targets, they always crit you. didnt have any good experiences with this. its a tactic game. if you like them, you'll like this. if not, you wont, not much at least.
final fantasy tactics advance (gpsp kai) on the other hand is easier, less annoying in the hit and miss department and mostly, you have different races which make your guild more colorful and interesting. boss battles and the rule system can be annoying at times. story is kinda meh.
and i think that could be all of them
my recommendations: play 9, then 6, then crisis core, then 7 and maybe 5. then pick whatever.