I've settled into Sildenafil which I get from Dr Fox and it seems reasonable and discreet, although I do try and make sure the delivery is going to be when I can check the post before the OH.
Started with 25mg by splitting the tabs (latest ones are 100mg but conveniently cut into quarters already). This was OK, but I've now decided to go for 50mg at least 1 hour before the punt and always make sure to drink at least 1 litre of water. I can sense the nose getting a bit stuffier, but never experienced a headache or other side effects and psychological or not, have had a solid punt ever since I started. Prior to this, I had at least two occasions where I either had a semi and came within about 10 minutes or actually shrivelled up after 30 minutes but was fortunate to be rescued with a lot of lube and an expert HJ.
It's all a very personal experience and preference, but my 2p worth is that if you have no medical conditions that suggest a problem and you are getting on a bit, it is well worth investing in the blue pill to ensure you make the most of your hard earned