Here is a list of some songs that give me similar feelings that Portishead does. They are not exactly like Portishead, but IMHO definitely worth a try.

Massive Attack - Unfinished Sympathy, Massive Attack - Teardrop, Röyksopp & Alison Goldfrapp - Impossible, Röyksopp - Vision One, Saint Saviour - This Ain't No Hymn

Massive Attack is closer to Portishead, but they don't have female vocals on all of their songs. Röyksopp goes to a bit different direction but they have many songs with different female vocalists that might be something you like.

[–] Uli@sopuli.xyz 3 points 9 hours ago

Might also try Zero 7. Their earlier albums feature vocals from Sia and Sophie Barker, as well as José González. All three have smooth evocative voices.

Sia: Destiny, This Fine Social Scene, The Pageant of the Bizarre, Speed Dial No. 2

Sophie Barker: Spinning, Passing By, In the Waiting Line, In Time

José González: Futures, Left Behind, Today, Crosses

These were all among my favorite songs almost two decades ago, when Trip Hop was at its height. Some I would still consider to be pinnacles of music.

[–] Vinny_93@lemmy.world 3 points 12 hours ago

Massive Attack ft Hope Sandoval (Mazzy Star) - Paradise Circus

Massive Attack ft Hope Sandoval - The Spoils