If I'm understanding where your pain is then it does not seem to be the RCL . If it's at the top of thumb and the base that is more symptomic of other issues like Dequervains ( tendinitis ) or osteoarthritis . That being said without the proper hands on evaluation that can not be fully determined . Often the main tenderness with RCL is on the outside lower part of the thumb . You could get a neoprene splint which includes the thumb and avoid sustained grips and pinches until you see the proper person to fully assess the situation . There are more rigged splints but those could be more hurtful then helpful without knowing what's really wrong .These often have metal stays and allows to much motion while trying to limit some actions . This could create problems so be careful with those .