There are several holsters that a similar to a T-shirt you could try. You could switch to a different type of outer garment or buy an IWB holtser. If you are dead set against wearing a "hip" type holster. Ankle carry?
I am a woman but hip carry during summer days...I wear a fisherman's vest for summer or thigh carry if wearing a dress. Either way, I feel comfortable without sacrificing too much. If I have to really go out somewhere posh, I layer my clothes...
Anyway, welcome to this group. I hope you enjoy your stay here...
You didn't mention what firearm you intend to conceal so without additional information from you a good answer is difficult.
Go on line and Google concealment holsters and see what comes up.
I'm going to assume when you refer to a 'hip holster' you are referring to an 'outside the belt' hip holster.
Personally, living in Central Florida it is hot or warm 3.5 out of 4 seasons so comfortable concealment is essential. I wear a Crossbreed super tuck carrying an XD40 4". Covers very well with just a baggy T shirt.
I saw a concealment rig that is worn like a belly pack but is worn inside the pants and hangs in the front above the crotch area. Forget what it is called but something like that may suit your needs.
I am a slim female, and I conceal a gun during the summer with just a slightly roomier shirt using an IWB holster. My holster is a custom holster made by UBG Holsters. I have heard nothing but good about the Crossbreed holsters, and many forum posters report that they can conceal mid-size guns easily using that holster.
I carry a Kahr MK9, which is VERY thin. I carry in the appendix position as I like that the gun is easily accessible standing or sitting (like in the car), and because I do a lot of lifting and reaching my gun won't print like it would if I wore the gun just behind the hip.
Behind the hip is a great place it carry if you are NOT bending or reaching a lot. The curve of the spine hides the grip (grip should be pointed toward your spine so that the draw does not sweep the muzzle toward your body), and draw is quick and effortless. I carry my larger guns in this position, again with just a slightly roomier shirt with a hem that lands below the beltline.
I am reasonable slim at 6"1" and an even 200. I wear IWB with a full sized 1911 in a tuckable holster. It is comfortable and rides well all the time. I hot weather I can just wear a tank style undershirt to keep it off my skin than a light shirt either tucked on not.