slav defense, black's bishop early development punishment After:

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1.d4 d5 2.c4 c6 3.Nc3 Nf6 4.Nf3 Bf5


I want to put a lot of pressure in black's position, I used to follow the game with:

5.cxd5 

And here black has two major options:

i) 5... cxd5

rn1qkb1r/pp2pppp/2p2n2/3P1b2/3P4/2N2N2/PP2PPPP/R1BQKB1R b KQkq - 0 5

5... cxd5 6.Qb3 Qb6 7.Nxd5 Qxb3 8.Nxf6+ exf6 9.axb3


I think it's very good for white

ii) 5... Nxd5, and here I found searching in a database a move that looks like strong, Nd2!

rn1qkb1r/pp2pppp/2p2n2/3P1b2/3P4/2N2N2/PP2PPPP/R1BQKB1R b KQkq - 0 5

5... Nxd5 6. Nd2 e6 7.e4 Nxc3 8.bxc3 Bg6


And in this position white has a solid center and looks for me a little better

I want more, how should I continue after 4...Bf5?
As far as I know it is consensus that the two variations you gave starting with 5.cxd5 are indeed the best possible way to play as White.

Now 4. ...Bf5 is a bad move, as Black is either forced to give up a pawn( in the first variation) or give up the center(as in the second variation), but despite these tactical flaws it is still a sensible developing move, so you really should not expect to gain more than you do in the given variations.

That being said, White does have different options available, but none of them is actually objectively stronger. In fact, if White is careless this variation can easily result in an equal or even slightly favorable position for Black. There is a famous game Yanovsky - Capablanca, that beautifully illustrates this danger.