Aim for recipes 6 to 8 ranks higher than you: this strikes a decent balance between success rate and reward. As a general rule, I would move on after SP drops to below 300 now, unless the synth is profitable or useful to you.

At 30 (currently 33) I started doing Velveteen dyes (37), this alongside Linen dyes (39?) should supplement you for this rough stretch. Having a Botanist friend or being one yourself is a decent alternative to fishing, moreso if you do both. Plan on doing Dart Frogs to Disabling Powder at 39 (47 recipe. Other sites are reporting falsely since I'm told this can't be attempted until 37).