The other half: when you do change things, change them big enough that you do not need statistics.
A test exists to detect a difference too small to see. At your size, the changes worth making are the ones that are not subtle: a completely different positioning, removing a required field, cutting three steps out of onboarding, changing who the page is addressed to. If a change is real it will show up in the monthly numbers without a significance calculation, and if it needs a calculator to see, it was not worth your month.
How to run that honestly without a testing tool:
Change one thing, and note the date. Compare a month before against a month after, and look at the direction and the size rather than a p-value.
Watch a longer window than feels necessary, because your monthly numbers are noisy too. One good month is not evidence.
Write down what you expected before you ship. This is the single most useful discipline available at small scale, it stops you from reinterpreting whatever happened as a success, which is very easy to do with forty data points.
And track the whole funnel rather than the one number. A headline that raises signups and lowers activation has made things worse, and at your size that trade is common and easy to miss.