Trouble Maintaining A Strong Erection In Certain Positions

I have always had trouble maintaining a strong erection in certain positions. Lying down and standing up come to mind. I am always strongest when sat upright, or when having sex in the 'bulldog' position. I have always felt this was strange and would love to feel at my fullest in other sexual positions. It helps to push down on the area above and below my penis. Does anyone have any recommendations for maintaining a more full erection? Aside from a cock ring which I have had a bad experience with, I do not 'lift' so I can presume perhaps a lack of testosterone.

I can only remember once in my whole life experiencing a rock hard erection whilst standing, maybe 3 years ago. Maybe I was particularly aroused, I don't know, but never since then. It felt great at that time and I would love to get that way again.

I have a fairly regular sex life and just feel like it's a pain me to have to prioritise one position over others; its like I cannot be spontaneous because my erection will not be as strong. For example, my penis is roughly 1 inch thicker around the head than the base. As a result, my partners tend to like me at times using just the head when inserting in and out. This I often use to heighten their orgasm (whilst also stimulating clitoris). But the only way to sustain a very hard head is for myself to push down on the area above my penis. I would love it if I could just do all this without that and be more attentive to my partners with my own hands.