Any after market seat is going to require the after market brackets, or if you are handy w/welder and fabricating modifing the stock brackets to fit the new seats.

If you are only looking to upgrade your worn seats and not spending $3-600, look at replacing them with some Celica, MR2, Supra(require more nods than Celica/MR2), or 2nd/3rd gen truck and 4-Runner seats. Everything but the Supra seats should be just about a direct bolt in, and shouldn't run you more than $100/pair.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed