G'day Placebonaut,
First of excellent decision to pick up regular exercise. I'd like to share some things that might be helpful.
1. Your diet and eating habits will impact how hard it is to get off that couch (amongst every single other thing in your life). I don't want to push you away with jargon but if you can crank the protein up, start to cut back on fast carbs (sugar, processed snacks) and maybe switch to a low sugar drink (vodka+diet mixer for example) you'll have an easier to time getting off the couch. It's adding more effort on I know, but diet is king for all from bodybuilders to office workers to drug users. Food isn't so unlike drugs in that what you put it determines how you feel. Cannot stress this enough.
2. Weight Training. Getting a bit ahead of you here and off track but If you really want to swap drugs for exercises 1-for-1 long term you might find more results in chasing the biggest rewards. The biggest rewards come from heavy intense work (short sprints or compound excercises. These spike all sorts of lovely hormones, endorphins and neurotransmitters that feel great. For now just getting out and going for a walk is plenty and you're doing fantastic, this is just to let you know that if you want to go down this path (and trust me you do) that this direction will net you even more results. You mentioned you may have some weights lying around, here are some exercises to google that you can do at home that cover multiple muslces = less time (i'm a intermediate bodybuilder and i only spend 30 mins 3 a week in the gym). Nothing wrong with bicep curls but they are one tiny muscle, we want to mainly focus on hitting our largest muscles and multiple at a time; Goblet squat, split squat, Romanian deadlifts, bent over rows, push ups, dips+pullups (might need to walk to a park for these but they are invaluable). Even just picking 2-3 of these twice a week and banging out 2-3 sets of 5-12 reps, whatever you feel like. Start lighter than you think and just get used to doing the movements for a month, don't worry about challenging yourself at all for now, just show up. But look into weight training, it's the gateway drug from running that hits much harder and it doesn't have to be that difficult or complicated, but does require a bit of learning. That's on you.
3. It. Gets. Easier. The first 2-3 months are the hardest. It'll take some time for your body to learn how to use it's muscles properly and some things (split squats) will feel damn near life threatening the first 2 weeks. You're going to be proud of yourself a bit and you are going to get the mental boost but there's so much more to come. Shirts fit better. Guy in the mirror looking less shabby. It's always going to take you to make you do it but once you're in this game for a few months you get more and more reward. I shouldn't mention this in the recovery forum but this also does include that your highs will 100% improve, I'll bring this back around by saying it's a good opportunity to decrease dose.
4. Excellent fucking work my friend. Exercise is a long game that's hard to fuck up and everyone wins in the end. The complete opposite of most substances. The only thing you have to do is show up, even if all you can manage is to half ass the training and the diet you are still making massive progress, just takes a little longer. Also if you've got a friend that's into exercise, liaise with them. It's a lot easier to hold yourself accountable when you've got someone else to impress/talk about it with. I wish you all the best friend.
Final little note; I may receive some pushback on this but it is my opinion so take it with a grain salt. I lead a very sedentary life, outside of 90 mins of gym a week i'm mostly in the office or at home on the couch. I almost never do any cardio (outside of 4 mins in the bedroom once a month). Walking/running is hard and it whilst it's one of the best things to increase life expectancy and health, in my experience the effort to reward ratio isn't as great as weight training. Just honestly; I'm in lean athletic shape at 80kg and all I do is eat my meals and train 90 mins a week, I'm not fully recovered myself either. With walking/running you might put in hundreds of hours, improve your overall health and get a lovely mental boost, but it's a lot of effort for less reward. Nonetheless I always suggest both, or more importantly what seems to work best for you.
I'm a huge advocate for exercise in recovery/active users; if you or anyone else are serious about this or just want to ask a few questions feel free to DM me, happy to share simple meals, what worked for me or just simply all you need to do to reach your goal and how the process will look and feel.