I've gone through similar thought processes and have reached the conclusion that taking the ATPL plunge is just too great a financial risk. Partly the lack of earning whilst training (with a large mortgage etc...) and also the near certain paycut for several years. I'm not on your wages, but a look at e.g. Flybe payscales (who are one of the better payers I understand) will show you what a TP FO will earn.
When you add in sacrificing my final salary pension (two thirds final salary for life, retire at 51, much obliged) - my sums just don't add up.
If you're on £100K now, you're in for one seriously big lifestyle change for quite some time.