
Gabriel C. answered 07/01/21
Triple Bachelor's in Mathematics, Music, and Spanish
This is an interesting sentence. If your intent was to say that while thinking about leaving your job, you received a better job offer, then ''was thinking'' is best. Using the past participle ''was thinking'' indicates the actions are overlapping.
Otherwise, the past action ''thought'' works best because both actions would occur independently. The sentence would be better still if you included a participle, e.g., ''I thought about leaving my job after receiving a better job offer,'' as you have clearly indicated one action follows the other.