Welcome @ruralgal, sounds like you’ve had quite the diagnosis journey!
Like you, I have found the information on psoriatic arthritis in Australia to be pretty generalised - and I’ve honestly not found much that was useful on exercise. For me, it was horseriding I wanted to get back into. So, I feel your pain, because of course I looked at the advice online and went… well I like yoga, and that’s fine, but at the start I could barely even do modified sitting yoga, and I could not see how that would get me back on a horse.
I had a lot of tendinopathy, and very little joint swelling. A lot of spinal symptoms (though I was also blessed with large and small joints too!). I say had, because it is rarely an issue now. I am not sure if your rheumatologist has had much of a conversation with you about treatment options, but it is well worthwhile educating yourself. There is lots of great info on this site. In Australia, we first try out all the traditional DMARDs (Disease-modifying drugs like methotrexate and Leflunomide). These are fairly cheap for the government to pay for. If these don’t work well, then you should, fairly quickly (within 6 months of first starting treatment), be having a conversation with your rheumatologist about biologics. These are extremely expensive for the government to pay for (like $25,000 per year). As such, there is lots of paperwork and hoops to jump through to qualify for them. Australian Rheumatologists can be very conservative (both for financial and medical reasons) with these drugs, and I found some resistance initially to getting them prescribed for me. Please feel free to ask for further info on all this stuff - the Aus system is a bit finicky to navigate, and there are a few other Australians on here who have also successfully done this. Hopefully you will get great results from methotrexate and / or Leflunomide and won’t need to worry about these yet, but that wasn’t my experience.
I realise it seems like I have wandered off-topic a bit because I started on exercise, but I haven’t, not really. For me, I found that trying to do anything except that gentle yoga and going for a stroll was just impossible (sometimes walking more than 200m without a rest was impossible), until I got treatment that worked. At the start I nearly killed myself trying to exercise because all the advice kept telling me to keep doing it - I overdid it every time and just triggered off another inflammatory flare. So my experience was that until I at least got a medication that made a substantial difference (like 80% better - the first one for me was Enbrel), then the exercise was not terribly helpful. So do focus on finding out about medications, advocating for yourself, and getting yourself on to something that works.
For me that took 12 months, and my muscles were pretty much like jelly by that time. From then on I did a session with a personal trainer once a week, and committed to myself that it was never about the number of reps or weights I did, but if I showed up, I succeeded. I figured that this really was a marathon, not a sprint, and I had the rest of my life to get good at it! It took a long time, but after a couple of years, I realised one day I was really quite strong again.
I approached horse riding the same way. I went for lessons once a week (as I didn’t own a horse anyway), with a “successful” week being me showing up and getting on the horse. Even if I needed help to tack up, or get on. Now some years on I’m having great fun training an off-the track thoroughbred at my lessons and sometimes I have bad weeks - I just tell the instructor and we do simple flat work.
Everyone is different, but for me I find that the exercise usually causes a small inflammatory flare, even with good medication. I schedule my exercise so that I’m only doing one or two big sessions a week, with a big break in between. At the start, I would actually schedule it so that the day after the exercise was the easiest day of the week in terms of other obligations, because I would usually be shattered. That still sometimes happens if I go too hard!
Finally, I ended up on a similar dose of steroids for around 12 months too. They caused osteopaenia in my spine (at age 39), which was actually how I convinced the rheumatologist we needed to try the biologics and see if we could move me off them. I’ve got to be honest with you, the tapering process is really hard. But they are not good drugs to be on long term, they really aren’t. And they do not change the course of the disease, so the sooner you can get a DMARD that will help enough to get off them, the better.
Okay, I’ve rambled enough for now! Hope you find lots of useful stuff here 
