I think given that you were diagnosed and started meds at age 69 damage to internal organs for you is not a major concern. If lithium helps continue with it just have your bloods tested as per instructed. I personally wonder about medication I take them but I feel worse but given I have been psychotic on three occasions now it is simply a case of have to or I wont be here. This illness sucks beyond belief taking all your hopes and dreams with it.
But work with your psych and find what's best for you. As said though you are 69 so damage to kidneys I think is a worry you can forget.
I also agree about mindfulness - it sucks and I find it really hard work however others get some real help from it. KEEP FIGHTING, DONT GIVE IN TO THIS AWFUL ILLNESS.