I've mostly switched to caffeine pills when I need caffeine (which varies, usually I try to go caffeine free). For me I find 100mg is a good amount, though if I could find 50mg pills I would try that. My preferred source is "jet alert" since I couldn't really find anything else that wasn't just 200mg.

Also, I always use an L-theanine supplement when I take caffeine, it's amazing how much it changes things. Instead of feeling all jittery and agitated I just feel less tired and more alert. This is roughly the equivalent of just drinking strong green tea.

I am in the UK and here it is quite easy to get 50mg pills in any chemist.

The most common brand seems to be Pro Plus but they cost a bit so I shopped around and found cheaper generic brands on Amazon.

The cheaper brands (apparently intended for sports) come in 200mg pills which I break in half with a knife.

These work fine, but one thing I discovered is that I need to remember to drink water as some of the symptoms of dehydration are similar to caffeine withdrawal.

Look into time release variety. Much more even throughout the day as opposed to using all the caffeine in a matter of a few hours.