Symbols indicating dynamics are all relative! A f in one context might sound completely different than in another context. This means that you can use the symbols in a flexible way to convey your intent. If you have a sequence of crescendos, where each one lands at a louder level than the one before, then you could have them land at p, mp, mf or at mp, mf, f. An experienced musician will interpret f according to the context.
An alternative approach would be to set up the bowing to elicit the dynamics you want. The hairpin that contains the loudest sound needs more bow than the others. So you might want to have the first two bars be a down bow with the long slur as you have written it; then no slur for bars 3 through 6, with a marking to stay in the upper half in bars 5 and 6. It's a little "middle school" (i.e. "junior high school") to tell adults to use the upper half, but it's an option.