Complex sentence: During one such voyage in 1911 Gippius bought a cheap apartment in Paris (on Rue Colonel Bonnet, 11-bis); what at the time felt like casual and unnecessary purchase some years later became a straw that saved them from homelessness abroad.
Split into simpler sentences: During one such voyage in 1911 Gippius bought a cheap apartment in Paris (on Rue Colonel Bonnet, 11-bis). What at the time felt like casual and unnecessary purchase some years later became a straw that saved them from homelessness abroad.