Upgrading from double to triple crank set.

I takes a while to get used to but I don't think it's worth the money to change the crank unless you live in a really mountainous area. Buying a shifter+crankset can be pretty expensive.

I don't really know what you mean by missing the middle ring. I'm assuming you used to have the 52/42/30 combination that comes with most triples. In that case, you can get kind of close to the 42 ring by replacing your small ring with a 44. But then again, I don't know if you have a compact (50/34) or traditional (53/39) crank, and I don't know if you want an easier gear or harder gear, so please give us some details.

You can also change the gears by changing the cassette in the back, but that depends on what kind of gears you want.

Yeah, that huge gap in the gearing that comes from not having the middle chainring sucks, but you get used to it. 😉🙄

I am in a mountainous area and ride a double. I did switch to a 12/27 a few years back. I have everything I need even on a 22% grade.

Nowadays triples are getting rarer and are being superseded by compact cranks.
It is probably better to think about the actual gear ratios which you have available and see what you need to do to get the range of ratios you want. You can cover quite a big (or small) range these days by considering cassette and chainring choice.

Quoted post said:

In that case, you can get kind of close to the 42 ring by replacing your small ring with a 44

There is no need to have a 44 if you really want a 42, chianrings are available in this size.

Assume your old bike had a triple, since you mention "middle ring". Suggest you ride the bike a bit more to decide if you can live with the 34 middle ring. If not, changing to a standard road double with a 39 ring shouldn't cost too much: all you should need is a new crankset.

OTOH, if you do need lower gears for climbing, but decide you really miss your old 39 and 53 rings, spending the money to convert to the triple is worth it. The dealer might even give you a break on the components if you do it while the bike is still new.

BTW, I agree with you about the 39 ring. People I ride with say they like their 34/50 compacts, but to me the triple is a better option. I've only ridden a compact for a week on a rental bike, but it seemed I was shifting cogs a lot more, and often ended up crossed chained. Maybe it's just been to many decades riding with 42 and now 39 middle rings for me to change 🙂

Some people seem to "ride it all" without any complaints. A buddy here has all three cranks for his Trek Madone: std, compact and triple. He likes to do the "mountain challenge" centuries, and changes cranks several times a season to get the gearing he wants for each event.