Who is your audience? What is your target market or niche? If you're targeting a specific niche like home security then perhaps you only need to sign up to ADT and SpyBase so your products match your audience. There’s no point promoting eco-mattresses to your blog that’s focused on reviewing drones. Again, you could sign up to a network that has a few different options in your field of interest or just go straight to your favourite suppliers and see if they have an affiliate program.
However, be aware that you need to submit an application to most of these networks to be accepted. Once you're accepted in, you're often required to apply directly to the merchant afterwards. So there are two layers or gates that you need to bypass. That's also why it's important to build up your platform and create that emotional bridge between yourself and your audience before attempting to promote anything to them.
I’d stick with Amazon if I were you. All of my Amazon sites only have Amazon affiliate links. If you use Google Adsense display ads on your site, you’re literally taking people away from your site for the sake of just a few cents with these type of ads. If you direct them just to Amazon, then you have a greater chance of earning more money from that click.