Any recommendations for intensifying my natural hair color?

I'm looking to not bleach my hair but rather to bring out my natural hair undertones and shine by making them richer. I also need something that can help close the cuticles of the old babylights I had done that have grown out. I don't want to cut it all off since I don't want to shorten my hair too much. Is there a toner or gloss I should do, perhaps even a keratin treatment? I have a cross between golden blonde and strawberry blonde hair that is medium to dark according to others. should I consider doing lowlights over the babylights and if so, how many shades darker and what color would make sense to bring out my natural dimension more? Thank you for your help in answering this.