d4 would be the best choice as white, for sure - generally leads to more positional situations.
Against the slav-
Exchange Slav is an option if you aren't annoyed by the drawish nature.
Against the QGD-
Exchange QGD (with a Nf3 0-0 setup like Karpov) is a good option.
You should probably avoid the Nimzo and Benoni (so, after d4 Nf6 c4 e6, play Nf3, and after d4 Nf6 c4 c5, play Nf3).
Thus, you'll have to learn the Queen's Indian, Bogo-Indian, and the line d4 Nf6 c4 c5 Nf3 (which transposes to a line of the Symmetrical English)- none will be too difficult to find something against that you like (main lines should suffice).
Against the Dutch, you can pretty much do the main line and it'll suit your wishes.
Now, as black- my recommendation would be the Caro-Kann, with a couple notes: 1) play 3...c5 against the Advance variation, as there are m any sharp lines if you play the main line Bf5. This appears to lose a pawn, but black has few issues getting it back. 2) It might be worthwile to play a sideline in the 3. Nc3 line such as 4...Nf6 or 4...Nd7 instead of 4...Bf5.
Versus d4, I would choose the Chebanenko slav (d4 d5 c4 c6 Nf3 Nf6 Nc3 a6) - a good video on it can be found here
This has the nice bonus of having a built-in rep vs c4, since you can just reply c6.
There are good courses on chessable for both of these defenses.
Personally, I've played almost all of this repertoire and have found it to be both good and positional.