plant shade trees to the south and wait a few years for them to grow?

I lived in one of those old 3 deckers that you see all around old cities in the NE US. They were built in the 1930s-40s. It was so drafty that in the winter I could literally feel a breeze coming from gaps around the walls.

My house has a basement that is so much cooler than the outside in the summer that if I put on glasses that have been sitting down there and head outside I'm blind from condensation. lol

using real timber so it’s probably not going to fall down

Nothing wrong with today's lumber, but there's a lot wrong with antique building standards of the 1920's + lack of code enforcement + old carpenters attitude of "that's the way it's always been done" if they even knew the current/correct rules in the first place.

A lot of near furniture grade lumber was used in old houses because it was common and cheaply available- unlike now. But there is no special advantage to using it in old houses for structural purposes. Today's houses are as engineered as automobiles are for cost and safety.

I’m there with you, only difference is my house has tongue in groove wooden interior walls.

Yeah short of the insulation blowing between the studs like you said with stabbing holes ... The other option is just replacing the plaster and lath at some point and when you do blowing insulation then. That's a huge remodel though.

There's definitely pros and cons to older houses, I bet if it's made of those materials it has a cool layout and flavor.

I live in a place that was built up through the late 80s through mid 90s so the houses have a lot of variety. Feels like once the 00s hit and especially the 2010s single family home neighborhoods all became the same house copy + pasted.

It was still an issue, the problem was either you just didn't have the knowledge and/or money to deal with it, were working with bad scientific beliefs based on real problems that were solved differently, or just lived in what used to be a much more mild climate.

In especially the 1930s-1950s the poisonous construction materials did in fact have slowed effects when you had a drafty house, so it became practice and advice to not fully insulate the home, to not create a sealed environment since the homes that did have good insulation and a good seal generally had more 'mysterious' deaths that were attributed to 'stale air' and even brought back the term 'miasma' for a while. It was gas/lead/asbestos/arsenic/CO/CO2/Radon poisoning. But back then they had correlation and used it as causation because why would air ever hurt you.

That and for the most part you had trouble keeping the house warm, not the opposite problem, so the cheapest and time tested solution was more blankets and a stone fireplace for part of the year and just deal with the outside temp the rest of the year, even on really hot days like the record breaking Chicago high of 102 in 1918 where the average was, you know, 80 for the several decades before and after that.