Well the Tories have a net loss of 7 MPs from byelections so far (lost 8, gained 1). Parliament's website claims they now have 352 MPs and a working majority of 60 (
link). But if I've counted correctly, there are another 5 MPs who were elected as Conservatives but who've had the whip withdrawn (Peter Bone, Matt Hancock, Scott Benton, Julian Knight, Rob Roberts) plus 8 DUP and 1 Reclaim (Andrew Bridgen - defected from Tories) - all of whom will probably vote with the Tories on most issues. If my maths is correct, that gives them an effective working majority of 88, so they'd need to lose another 44 seats at by-elections in order to force a change of Government without an election. (Though in practice, if they did lose that many, the more likely result is them losing a confidence vote in Parliament triggering a general election anyway).