Of course you want affiliates with high commissions, but they should also have a solid reputation with high conversions and low reversal rates (you get $0 if people cancel after signing up). If they’re part of an affiliate marketplace like ShareASale or ClickBank you can see some numbers there. Companies likes Amazon/SiteGround are safe bets, otherwise do your research (or track your affiliate links so you can monitor their performance). Avoid affiliates offering huge commissions since this probably means they’re struggling to acquire/retain customers naturally. This will hurt your numbers (specifically your conversions/reversal rates).
There’s a good reason why ClickBank is still a strong contender, however it does tend to focus more on digital products which may be of questionable quality. Yes, the review process is more professional these days, but it’s still primarily focused on selling digital products, especially “how to make money” courses and the like. That being said, there are some genuinely high-quality products on offer, and few affiliate programs are bigger than ClickBank, especially in selling (primarily digital) books.
It also shows that you need substantial traffic to make much money through advertising. At a CPM Of £10 with 2 ad units on the site, you would make just £4,000 per month even with a million page views per month for which you serve paid ads to 20% of the audience. Set this to 100% if you are selling all your ad inventory, as for example through Google Adsense.