Code P0301

My car is actually a Lexus ct200h, but since that model wasn't listed I entered under a Toyota Prius of the same year - 2012.

A few weeks ago I got the dreaded P0301 code. The first attempt to solve the problem was new spark plugs and a new coil pack for cylinder #1. A few days later the check engine light was on again and an accompanying rough start. This time it was cylinder #1, #2, and random misfiring. With the help of info on this forum I learned that the EGR system was a likely culprit, so I took it apart and thoroughly cleaned it. I held my breath for a week and assumed that was all that was needed. Four days later it was back, though the shakes weren't as bad. Current mileage is: 245,000kms/152,000miles.

Here are the symptoms:

Occasional rough start when cold.
P0301 code returns every few tanks of gas.
slight coolant loss (1 litre/quart per 1.5 tanks of gas).
compression in cylinder #1 = 115, cylinders 2, 3, 4 = 124.
when the engine is cold and the coolant reservoir is topped up there are approximately 20 bubbles per minute.

I tried to find a leak down tester to rent, but no one is renting or loaning tools in my area due to covid. And, I tried to mickey mouse an adapter to just force compressed air into the cylinder to be able trace the problem, but I haven't been able to get fittings to match. So, I'm wondering if that list of symptoms is enough to verify the head gasket is going, or could there still be other potential causes at this point? I know that 115 psi is still acceptable compression, and still within the acceptable difference range from the other cylinders. I really want verification before I spend money or time.