Baggers,
Your diagnosis, as far as you've given (PSA 4.22, G 7, and probably T2a or T2b) is quite favourable for a prostatectomy. Two bits of information are missing though - how near the edge it is, and if you are likely to be able to have nerve sparing so there's a chance erections will recover afterwards. If it's near the edge, that reduces the chance of the prostatectomy working, and you might then also have to have RT, in which case you should consider having just RT in the first place. If nerves won't be spared and sex is important, again, consider RT as that has a better chance of preserving erections.
If you decide on RT as a primary treatment, there are a number of choices. EBRT (external beam) is what most people will think of first, but you may be suitable for a more closely targeted radiotherapy such brachytherapy (internal radiotherapy) or stereotactic radiotherapy (SBRT, or by a trade name Cyberknife), which are more precision treatments and come with fewer side effects. The downside of RT is that as a younger person, you have a long period of life ahead, and as RT treatments have a small risk of creating cancers decades ahead, that risk will be higher for you than for an 80 year old, where they aren't going to live long enough for that to happen.
As a T2a or T2b, you might also be a suitable candidate for HIFU where the areas of cancer are destroyed by High Intensity Focused Ultrasound. This is focal treatment (targets just the cancer), but is much less proven by data than the other treatments, due to far fewer treatments.
You will probably only be offered treatments which your cancer centre provides (or other centres linked to it). If you want to investigate something like HIFU, you would have to be asked to be referred to one of the hospitals currently trialing it on the NHS.