Yes you should buy a meter.
Without it you cannot see what each meal does to your bloods (and other things like exercise or illness). Once you have this information then you can adjust what you eat, and do, to control the levels.
@Bluetit1802 has info about good value meters if cost is the main consideration.
The basic tests would be before and 2 hrs after each meal, looking for a rise of no more than 2mmol and hopefully going no higher than 7.8mmol.
You can also choose to test at 1hr to see how high the spike does go (everyone’s will rise but diabetics fail to drop again hence the 2hr bit) or 3hrs to see if the levels return to normal if they haven’t yet or if the rise has been delayed as some grains or meals with fat are for some people
Edit: beat me to it
@Bluetit1802