Would a full frame option take me well beyond my current budget or would that be something to aim for long term?
Probably, but you never know what kind of deal you can make. I mentioned Micro 4/3rds because this is an Olympus forum, and I use it. There are plenty of other brands with larger sensors that are still less than full-frame. What is more important to you, stills or video?
For example, most lenses for sub-full-frame cameras won't work on the same company's full frame version. As a result, you will often see great deals on a metal housing, camera, and a great assortment of lenses when people are upgrading. Nikon and Canon are the most prevalent on the market. Are you interested in underwater macro or just wide angle? What about topside photography? Telephoto lenses are pretty nice topside.
Upgraders will often keep their strobes but they can be purchased used as well. A lot of flash-only strobes are being upgraded for flash & video lighting if video lighting isn't important to you.
On the other hand, you may only be interested in snapshots for your phone and social media. A smaller and simpler system may be a better choice. Your luggage gets heavier as you move up the resolution ladder. Like many things in life, zeroing in on "good enough" is a challenge.