Ok, back from getting my results. Hopefully this info may help others on here.
So, my lining is 8mm and their cut off is 4mm. However, she said she was "almost positive" it wasn't sinister, but she wanted a look anyway and asked if she could do a biopsy there and then. I knew from posts on here that it might be uncomfortable, but I went for it because otherwise it's more delay and worry and I just want this resolved.
On the way in she said her path was obstructed by a polyp - in fact she said "I KNEW IT!". She said she wanted to remove it, told me to count slowly for ten seconds and that she'd stop if neccessary. Actually, it wasn't so bad. Most uncomfortable bit was after that, when she pinched the uterus to remove the cells. That was like sudden, intense period pain which was really not nice, but it's quick and it's done and it's over.
I'm bleeding a bit and have intense period pain crampiness now but it's done. Outlook - if that actually is a polyp rather than just a chunky bit of endometrium, it means there are probably more in there which need to come out (so either general anaesthetic this time as there may be a few of them, and higher up) or I can be stoic and endure it like I did today. Not sure how stoic I can be if there are lots of 'em.
As she's fairly sure I'm not cancerous, she suggested having a mirena coil fitted once we've resolved the polyp situation.
The takeaway for anyone going through this - get to a doctor even if it's just a small amount of spotting. Having a polyp removed is uncomfortable but nothing to be scared of. A biopsy is less fun, but it's at least relatively quick (15-20 seconds). Fingers crossed her prognosis is correct and it's nothing serious, and she stressed that visiting the doc is absolutely the right thing to do as any early stage endometrial cancer is very treatable.