Much of this was inspired by Inuktitut, but it sounds very different without uvulars.
https://www.youtube.com/watch?v=SAwyQJ33jyoI made some improvements:
/p/ = [p] ≠ [pʰ]
/t/ = [t] ≠ [tʰ]
/k/ = [k] ≠ [kʰ]
/j/ = [j]
/n/ = [n], [ŋ]
/s/ = [s], [s̠]
/w/ = [v]
/l/ = [l̥]
/m/ = [m]
/u/, /o/ = [ʊ], [u], [o]
/i/ = [i], [ɪ], [e]
/e/, /a/ = [a], [æ], [ɛ]
When two syllables with i follow each other, the initial one is often [ɪ]. For example; lili, ni li, kili.
When n comes at the end of a syllable it would be pronounced as [ŋ] (linja, jan, anpa), and [n] in all other cases (sina, ni, ona). I believe that this would be slightly easier to pronounce than just [n] in all situations. (n-n = n) (n-vowel = ŋ)
Stress:
The syllable before punctuation.
e, li, la, pi
mi and the na of sina when it is used like "you are" and "I am".
Diphthongs and vowel length:
When a word beginning with a vowel follows a non stressed word ending in a vowel, the two would usually form a diphthong or a long vowel:
a-i, e-i = [ai]
a-u, e-u, a-o, e-o = [au]
u-i, o-i = [ui]
o-e, o-a, u-a, u-e = [ua]
i-a, i-e = [ia]
i-u, i-o = [iu]
o-o, u-u, o-u, u-o = [ʊː], [uː], [oː]
a-a, e-e, e-a, a-e = [aː], [æː], [ɛː]
i-i = [iː], [ɪː], [eː]
If the word following an e or a is "e", it would become [ai], instead of [aː], [æː], or [ɛː].
This was just a concept I came up with, it's probably a little bit too much of a stretch to be added to toki pona. Another way to do it would be to just keep consonants and everything else the way it is, but use the three vowel system for pronunciation, which I think really would improve it.