Deducing from other posts that you are living between Elmstead Woods station and White Horse Hill, if the buses and trains match tolerably, the 273 and St Mary Cray looks the best. The combination of 162 and Bickley would work from other parts of C'hurst.
I don't know the 273, but the 314 now takes a devious route into Bromley and then tangles with the town centre "bypass" traffic.
I wouldn't rely on a tight connection shown on NRE at Petts Wood on the all-rail route as trains towards Victoria are likely to be "right time" and there's not always a cross-platform interchange (BTW - the footbridge is at the London end there).
I think the only thing to do is to trial it. If you are a cyclist, you could check out cycling to SMY or BKL - the latter is off main roads, but it's all surprisingly hilly!