iOS upgrade on older, but perfectly usable iPhone

Please advice; would upgradeing iOS on my still-totally-usable iPhone 6 - from current 10.3.3 to recently suggested, 12 cause any negative result? Last time I follow upgrade suggestions on iPhone 5, upgrading the iOS actually made it necessary to buy a newer iPhone. I just don't want to have to give up using my current iPhone and spend hundreds of dollars for new one for that reason: as it would make me feel tricked, again.