I believe you have answered your own question. Yes, perhaps you should consult a patent attorney.
As for the drawings of this "simple" device, how hard would it be for you to make either a working or non-working prototype? If you can do so at relatively low cost then taking it with you when you see the patent attorney would be extremely helpful and perhaps save you money.
As to the concern that someone will improve the design after you patent it, don't worry. If the improvement relies on your patent they can not sell it without your permission. If they wanted to sell something without your permission they would have to invent an alternate device that did not infringe on your patent. As a concrete example, supposed you invented the wood screw and then they improved it by using a phillips head. They still could not sell their screw without your permission. If on the other hand they invented nails, they could sell nails because nails are different than screws.
A good patent attorney specializing in medical devices will be able to help you craft your patent application in such a way as to minimize the chances of an alternate device being developed that would not infringe on your patent.
EDIT:
Since you say you could probably make a prototype I recommend you do so. Keeping your eye on the prize, which is to make money, this will be the best thing to both advance your patent claim as well as move you closer to revenue. At this point properly documenting your invention and establishing a "first to invent" claim for a United States patent is critical. Note that in other countries "first to file" is generally the rule.
By making the prototype you are doing what is termed reduction to practice.
In United States patent law, the reduction to practice is a concept
meaning the embodiment of the concept of an invention. The date of
this embodiment is critical to the determination of priority between
inventors in an interference proceeding.
Conception is the "formation in the mind of the inventor, of a
definite and permanent idea of the complete and operative invention,
as it is hereafter to be applied in practice." Hybritech Inc. v.
Monoclonal Antibodies, Inc., 802 F.2d 1367, 1376 (Fed. Cir. 1986)
(quoting 1 Robinson On Patents 532 (1890))
The embodiment of an invention can either be:
Actual reduction to practice: "[R]equires that the claimed invention work for its intended purpose." Brunswick Corp. v. U.S., 34
Fed. Cl. 532, 584 (1995).
Constructive reduction to practice: "[O]ccurs upon the filing of a patent application on the claimed invention." Brunswick Corp. v. U.S.,
34 Fed. Cl. 532, 584 (1995).
"Simultaneous conception and reduction to practice": "In some instances, such as the discovery of genes or chemicals, an inventor is
unable to establish a conception until he has reduced the invention to
practice through a successful experiment." The Regents of the
University of California v. Synbiotics Co., 849 F.Supp. 740, 742
(S.D.Cal., 1994) (citing Amgen, Inc. v. Chugai Pharmaceutical Co.,
Ltd., 927 F.2d 1200, 1206 (Fed. Cir. 1991)). The court will apply this
doctrine in so-called "unpredictable arts" such as biology and
chemistry where the invention is a "biologically active composition of
matter," also called a "bio-chemical substance."
Don't be confused as to the purpose of patent drawings. Their real purpose is to disclose as little as possible about the actual invention and obstinate as much as possible. Creating good patent drawings is a highly specialized art for that reason. You absolutely do not want drawings that disclose everything and make it easy to copy. Your patent attorney will help you.
Do you know a surgeon you can trust not to steal your idea? If so, show him the prototype and get his opinion, preferably in writing, as to it's utility and value. This will also help you with your patent claim.
Remember the goal is not simply to get a patent but rather to make money. You also want a good patent that will stand up and offer the best protection.
The patent office is full of thousands of patents for devices that were never made or profitable. There are many, many patent attorneys who will gladly take your money to get a patent that will ultimately be worthless.
Make the job as easy as possible for your attorney; you will get a better patent and save yourself a lot of possible litigation down the road if you should need to defend your patent.
