DIY AC Top Up

So I got my car over a year ago now, back in March where temps were pretty low, the AC blew cold air but only slightly, I haven't had the time or really a need to diagnose/fix it. However now with the current heat we are getting in the UK, heatwave after heatwave need to get on top of it. As it feels like it's basically not blowing anything cold at all.

Read a lot of posts/forums here and elsewhere. There was a mention here that maybe the expectation from the system is a bit much, however, I air the car out whilst driving (several minutes windows down), turn on the AC, put on auto mode and keep the fans blowing slightly above half speed max and as that drops, I slowly incrementally drop the temperature to adjust. I still need to check the sight bubble and "diagnose". Also in comparison to other Prius cars that family members have sat in, they state they are super cold and AC kicks in immediately so clearly there must be something up, leak or low on refrigerant.

Now I have 3 options, direct dealership for about £180.00, other garages £150.00 or mobile mechanics around £60.00-£100.00 or DIY route about £50.00.

I am aware of the oil type that can be present in some refrigerants and which to avoid etc. Safest route would be dealership, however I don't want to end up spending £180.00 to find out there is a leak and not have a working AC. Doesn't make sense for me to go to other garages that are charging near dealership prices otherwise I would do that. In regards to mobile mechanics, I honestly don't believe they would have separate dedicated machines/pipes for normal cars/hybrids/refrigerants so some contamination would 100% occur which is not worth the risk.

I will first do my due diligence and try to diagnose using the sight bubble if it's apparent that the refrigerant is low. Will look at purchasing just the refrigerant itself with no additives as found some online that are hybrid safe/don't have any additives.

Has anyone gone ahead and DIY topped up their system?