I haven't had the experience of the mortgage side, been in rented since splitting from the ex. But i would imagine if i was in that situation and planning to go BR very soon i'd just tell them what my intentions are. Probably get yourself a date first for your BR though. Just my thoughts i'm no expert in this so you might just want to get some professional advice first.
You will be fine it just probably all feels a bit daunting right now but it really does get easier i promise.