I have not done the DIY CO2 thing so be aware of that? But I would feel that there is a basic reason we don't see the combo of DIY and solenoid too much. DIY is almost automatically cheaper while a good solenoid is definitely NOT cheap, so less often combined. But not a reason for not doing it if it appeals to you.
One thing I would recommend is getting something that can be reused/ repurposed if you should decide cO2 is worth going to pressure.
So the main question is getting a solenoid that is good and will last and also can be done with compression fittings to get better grip on the tubing. My choice for this would be to shop E-bay for a Clippard Mouse series solenoid and then combine it with a Clippard manifold to let you use hard plumbing which gets you into the far more common 1/8 inch fittings.
The solenoid is pretty common on the site but I never see the manifold which leaves that part more difficult to acquire, maybe even going to a distributer.
Shop carefully for the correct solenoid as there are many which DO NOT do work for our use.
ET -2M-12 is my favorite , ET gives terminals for the wires, 2M is 2 ports (in/out) and mounted on a manifold. 12 is 12VDC
EV- wires but thin ones?
-24 at the end needs 24VDC supply
Again , please shop carefully as it can be a minefield if you are not careful and correct!!!
The manifold is 15490-5----
shown here but hard to get: