I’ve been in a very similar position recently, so I completely understand the challenges you're facing. We owned our previous home outright too, but due to a few local planning disputes, we couldn't sell at the time we found our “dream home.” Like you, we were looking for something that worked more like a bridging loan, but without the formal structure and high fees that typically come with it.
What ended up helping us was working with a mortgage advisor who specialised in complex cases involving second properties. We explored a couple of options, and while some high street lenders were hesitant, smaller or more flexible brokers had access to lenders who were willing to take a more holistic view, especially since we had no existing mortgage debt.
You’re right that lenders can get confused between second home purchases and buy-to-let scenarios. What helped was clearly demonstrating our exit strategy (i.e. sale of the first home within a set timeframe), and showing we had reserves in place to manage both properties temporarily. Stamp duty was steep, but like others have said, we reclaimed it once the sale went through.
If you haven’t already, you might want to check out the Property Store. They’ve got a good grasp of current market conditions and can help you explore creative financing solutions that aren’t always obvious to larger institutions. I found their insights really useful when navigating the same second-home puzzle.
Wishing you the best of luck, it's a juggling act, but definitely doable with the right support in place.